Causation in Professional Negligence Claims: Why Is Loss Hard to Prove?

Key Takeaways

1. Causation in professional negligence claims is the legal link showing that a professional’s breach probably caused your loss.
2. The “but for” test asks whether you would have suffered the same loss if the professional had acted competently.
3. Proving a breach of duty is not enough if the same outcome would probably have happened anyway.
4. Courts reconstruct what would probably have happened with competent advice, which is difficult where markets, third parties or your own decisions intervened.
5. Preserve emails, advice, file notes, accounts, transaction documents and valuation evidence to support the alternative outcome you rely on.
6. A lost chance must be real rather than speculative, with a rational basis for valuing it.
7. Act early to preserve evidence, mitigate your loss and obtain advice before limitation periods undermine a potential claim.
8. Go Legal is rated Excellent with over 300 five-star reviews and 5/5 on Trustpilot and Google, placing our solicitors among the best-reviewed litigation lawyers in England and Wales.

What Is Causation in Professional Negligence Claims and Why Is Loss Hard to Prove?

Causation is the legal link between a professional’s breach of duty and your loss. You must show, on the balance of probabilities, that the loss would probably have been avoided if the professional had acted competently, not merely that the professional made an error. Loss is hard to prove because the court must reconstruct an outcome that never happened: what your position would have been with competent advice.

That alternative outcome must be built from documents, witness evidence and expert analysis, often years after the event. The professional will usually argue that the same result would have followed anyway, because of the market, a third party or your own choices.

A professional negligence claim against a solicitor, accountant, surveyor, financial adviser or insolvency practitioner usually involves these stages:

1. The professional owed a contractual duty or a duty of care.
2. The professional breached that duty.
3. The breach factually caused loss.
4. The loss fell within the scope of the professional’s duty and was not too remote.
5. The loss can be quantified, subject to mitigation, contributory negligence or another contributing event.

Proving breach does not prove loss. A claimant may show that advice fell below the required standard but still recover little or nothing if the same outcome would probably have occurred with competent advice.

Damages aim to put you in the position you would have occupied if the professional had performed the retainer properly. They are not intended to provide a windfall.

Our solicitors advise individuals, directors, professionals and businesses across England and Wales on professional negligence claims. Book a free consultation or call 0207 459 4037.

Who Can Bring a Professional Negligence Claim in England and Wales?

You may have a professional negligence claim if you relied on professional advice or work, suffered loss and can show that the professional owed you a contractual duty or a duty of care.

Claims commonly involve:

• Solicitors who mishandled litigation, transactions or deadlines.
• Accountants and tax advisers who gave incorrect financial or tax advice.
• Surveyors and valuers who prepared defective reports or valuations.
• Financial advisers who recommended unsuitable investments.
• Insolvency practitioners whose decisions affected company assets or creditor recoveries.

The retainer or engagement letter matters. It shows what the professional agreed to do and which risks they were engaged to address, which later shapes what loss is recoverable.

Claims are brought in the High Court, including the King’s Bench Division or the Business and Property Courts, or in the County Court, depending on factors such as value and complexity.

A liability cap or exclusion clause may also affect recovery. Under section 2 of the Unfair Contract Terms Act 1977, liability for death or personal injury caused by negligence cannot be excluded or restricted. Liability for other loss caused by negligence can be excluded or restricted only if the term is reasonable.

Why Is Proving Loss in Professional Negligence Claims So Difficult?

Proving loss is difficult because you must establish a better alternative outcome, often years after the advice or transaction. The six main practical hurdles are:

1. The court must reconstruct an alternative reality. It compares what happened with what would probably have happened if competent advice had been provided. That scenario may depend on decisions by you, a purchaser, lender, investor, court, HMRC, company board or another professional.
2. Several causes may have contributed to the loss. Market conditions, commercial decisions, third-party conduct and your own actions may all have affected the outcome.
3. A lost chance is not a guaranteed result. A missed opportunity to settle, buy property, raise finance or bring a claim must be shown to have been real rather than speculative.
4. The underlying claim may need to be proved. In solicitor negligence claims, the court may need to assess the prospects and value of the original dispute.
5. Mitigation can reduce damages. Failing to take reasonable steps to limit loss may reduce the amount recovered.
6. Evidence deteriorates over time. Files may be incomplete, memories fade and commercial records may no longer be available.

How Do Courts Reconstruct What Would Have Happened With Competent Advice?

The court asks what would probably have happened if the professional had acted properly. That can involve several uncertain decisions: whether you would have proceeded with a transaction, whether a lender would have provided finance, or whether HMRC would have accepted a particular tax treatment.

You must support the proposed alternative outcome with evidence. A statement made after the dispute began usually carries less weight than an email or board minute created at the time.

What Happens When Several Causes Contribute to Financial Loss?

A professional is not automatically responsible for every loss that follows a mistake. You must show that the breach was an effective cause of the loss claimed.

The court will separate loss caused by negligent advice from loss caused by market movements, a failing business, a third party, a later decision or an independent event. It will also ask whether the loss falls within the scope of the professional’s duty, a point the Supreme Court has addressed directly (see below).

Can You Claim Damages for a Lost Chance?

You may recover damages where negligence deprived you of a genuine opportunity. You must:

1. Identify the opportunity that was lost.
2. Show that it was real rather than speculative.
3. Provide a rational basis for valuing it.

The Supreme Court’s decision in Perry v Raleys Solicitors shows how this works. Mr Perry alleged that Raleys Solicitors’ negligent advice on an industrial-disease compensation scheme deprived him of the opportunity to claim a Services Award. The Court held that he had to prove, on the balance of probabilities, that he would have acted differently if properly advised and that the lost opportunity caused loss. As the Court put it:

“The onus is on the claimant to establish causation on the balance of probabilities.”

Where the beneficial outcome depended on what third parties would have done, the value of that chance was assessed on a loss-of-chance basis. The Supreme Court allowed Mr Perry’s appeal and restored the County Court’s award of £14,556.15 plus interest.

The practical lesson is that your own likely decision must be proved as more probable than not. Only the uncertain decisions of others are valued as a percentage chance.

What Is a Case Within a Case in Solicitor Negligence Claims?

A “case within a case” arises where you say a solicitor’s error caused you to lose an underlying claim, settlement or transaction. You may need to prove:

• The strength of the original claim.
• The likely response from the opponent.
• The probable settlement or judgment.
• The financial value of the lost outcome.
• That you would have pursued the matter if properly advised.

These claims are complex because the court examines both the alleged professional error and the original dispute, which may itself turn on evidence that is now years old.

How Can Mitigation and Your Own Decisions Reduce Damages?

You must take reasonable steps to limit loss after discovering a possible error. This might mean selling an asset, obtaining replacement advice, challenging a decision, preserving evidence or pursuing an available remedy.

You are not required to take unreasonable or disproportionate steps. However, failing to act when a sensible remedy was available may reduce damages. Your own conduct can also lead to a reduction for contributory negligence.

Why Does Delay Make Causation Harder to Prove?

The most useful causation evidence is usually created at the time of the advice, transaction or decision. Emails, file notes, valuations, accounts and board minutes show what people knew and intended then. A reconstruction prepared years later, after a dispute has arisen, is easier for the professional to challenge.

How Does the But For Test Work in Professional Negligence Claims?

The but for test asks: but for the professional’s negligence, would you have suffered the same loss? If the loss would probably have happened anyway, factual causation is not established.

You must prove causation on the balance of probabilities, meaning more likely than not, or more than 50% probable, that competent advice or services would have avoided the loss. If the honest answer is “maybe” or “it’s complicated”, the claim is likely to fail on causation.

The court may ask:

• What would you have done with correct advice?
• What would a lender, buyer, investor, court or HMRC probably have done?
• Would the transaction, claim or investment have proceeded?
• Would you have negotiated different terms?
• What financial position would probably have resulted?

Evidence that a better outcome was merely possible will usually not be enough. This matters most where the alleged loss involves business growth, investment performance, litigation strategy, a hypothetical settlement or a failed transaction.

What Evidence Is Needed to Prove Causation and Financial Loss?

Your evidence must show what happened, what would probably have happened with competent advice and the financial difference between the two.

Useful evidence includes:

• Contemporaneous documents: emails, letters, advice, instructions, reports and file notes.
• Engagement letters: showing the professional’s role and responsibilities.
• Transaction records: contracts, invoices, accounts, bank statements and completion statements.
• Witness evidence: from you, directors, employees, other advisers and relevant third parties.
• Expert evidence: from a professional in the same field, addressing the standard of care, breach and the likely alternative outcome.
• Valuation evidence: property and business valuations, loss-of-profit calculations and investment performance analysis.
• Alternative-outcome analysis: modelling what would probably have occurred with competent advice, supported by contemporaneous evidence and expert opinion.

Each item should answer a specific causation question. A valuation may establish the size of a loss, while a board minute may show what directors would have done with accurate information. The evidence must also separate loss caused by the negligence from loss caused by market conditions, another adviser, a failing business or an unrelated event.

When Is Causation Disputed in Different Professional Negligence Claims?

The causation question depends on the professional’s role and the outcome you say was lost.

Solicitor Negligence

For a missed limitation deadline, you may need to prove that the underlying claim would have succeeded and what it was worth. For negligent litigation conduct, the issue is what settlement or judgment would probably have been achieved. For negligent conveyancing or corporate advice, the court asks whether the transaction would have proceeded and on what terms.

Accountant and Tax Adviser Negligence

The court may ask whether HMRC would have assessed the same liability even with accurate advice. For negligent audits or accounts, the issue is whether you would have made the same investment or lending decision with accurate financial information.

Surveyor and Valuer Negligence

You must usually show whether a competent survey or valuation would have led you to withdraw, negotiate a lower price or accept different lending terms.

Financial Adviser Negligence

You must show what you would probably have done with suitable advice. The court may consider your risk appetite, your instructions and the return a suitable alternative investment would probably have produced.

Insolvency Practitioner Negligence

You must show what recovery competent conduct would probably have achieved in realising assets or pursuing claims. You may find our guide on insolvency practitioner negligence useful.

What Do the Courts Say About Causation and Scope of Duty?

The Supreme Court has confirmed that factual causation is not the only requirement. The loss must also fall within the scope of the duty the professional assumed.

In Manchester Building Society, the Supreme Court explained the principle in these terms:

“The scope of duty principle is that a defendant is liable only for losses which fall within the scope of the duty of care assumed by the defendant.”

A professional is therefore not liable for every foreseeable consequence of reliance on negligent advice, only for losses resulting from the matters that made the advice wrong. In practice, ask what the advice was for and whether your loss flows from the risk the professional was engaged to address.

What Laws and Deadlines Apply to Professional Negligence Claims?

The usual limitation period is six years, but the start date depends on whether the claim is brought in contract or tort.

• Contract: Under section 5 of the Limitation Act 1980, a claim founded on simple contract must be brought within six years from the date the cause of action accrued. This is usually the date of breach.
• Tort: Under section 2 of the Limitation Act 1980, a claim founded on tort must be brought within six years from accrual. This is usually when damage occurred.
• Later knowledge: Under section 14A of the Limitation Act 1980, certain negligence claims where the relevant facts were not known at accrual may use either six years from accrual or three years from the statutory starting date, whichever expires later.

Section 14A does not extend every claim. Its starting date turns on when you knew about the damage, its attribution to the alleged negligence and the identity of the professional. A claim issued out of time may fail even where breach and loss are otherwise strong.

What Should You Do If Professional Negligence Caused You Loss?

Act promptly to preserve evidence, limit further loss and protect your position on limitation.

1. Preserve advice, emails, letters, reports, file notes and transaction documents.
2. Build a chronology of instructions, advice, decisions, losses and later events.
3. Identify the specific alternative outcome that competent services would probably have achieved.
4. Obtain replacement professional advice where necessary to stop the loss increasing.
5. Avoid deleting, editing or selectively sharing relevant documents.
6. Consider whether expert evidence from a professional in the same field is needed on the standard of care and the counterfactual.
7. Consider whether the professional has professional indemnity insurance or other assets from which a judgment could be satisfied.

We offer a free initial consultation for professional negligence claims, where our solicitors can give a preliminary view on breach, causation, loss and limitation.

Frequently Asked Questions

Speak to a Professional Negligence Solicitor Today

Causation is often the decisive issue in a professional negligence claim. Showing that a professional got it wrong is only the start. You must prove what would probably have happened with competent advice and the loss that followed, and the longer you wait, the harder that becomes as evidence fades and limitation runs.

Our solicitors assess breach, causation, scope of duty, evidence and limitation before significant costs are incurred. We act for individuals, directors, professionals and businesses across England and Wales and can help you understand whether your loss is legally recoverable.