Some cases matter because of the facts. This one matters because of the trap hiding underneath a question that sounds almost administrative: when a law firm changes its name, who actually owns its mistakes?

BDB Pitmans LLP v Lee, decided by the Court of Appeal alongside its sister case Adcamp LLP v Office Properties, answers that question in a way that will change how negligence claims are drafted for years to come. If you want a case that shows you understand civil procedure at a level most candidates never reach, this is it.

Pitmans LLP had, on the claimants' case, given negligent advice. Sometime later, Pitmans merged with Bircham Dyson Bell LLP. The combined firm went through a couple of name changes, becoming BDB Pitmans LLP and later Broadfield Law UK LLP. The firm's own published accounts stated that Broadfield had acquired the liabilities of Pitmans, and that Pitmans had transferred them across.

Understandably, when the claimants came to sue, they issued proceedings against BDB Pitmans, on the belief that BDB Pitmans had inherited whatever liability Pitmans held. There was just one problem. By the time this mistake came to light, the limitation period for the original negligence claim had already expired.

The claimants tried to fix this by substituting Pitmans (or its later incarnation) into the claim in place of BDB Pitmans. The defendants objected. And that objection is what took this case all the way to the Court of Appeal, with the Supreme Court now set to hear it too.

Substituting a party after limitation has expired is not something the rules allow freely. Section 35 of the Limitation Act 1980 and rule 19 of the Civil Procedure Rules only permit it where the substitution is necessary to the original claim, and where one of two gateways applies.

The first gateway covers a mistake as to name. If you sue "Smith Ltd" when you meant "Smith Limited", that is a naming slip and the rules will usually let you correct it. But that gateway was closed to the claimants here from the outset. Established authority, going back to Adelson v Associated Newspapers Ltd, draws a hard line between mistaking a party's name and mistaking a party's identity. The claimants knew perfectly well that it was Pitmans who gave the advice. Their mistake was believing that BDB Pitmans had taken on responsibility for it. That is a mistake of identity and belief, not a mistake of name, so the first gateway never applied.

That left the second gateway: whether the original claim could not be maintained unless the new party was added or substituted. At first instance, two different High Court judges took a generous view of this gateway and allowed the substitution, relying on obiter comments made over a decade earlier by Leggatt J in Insight Group Ltd v Kingston Smith.

The Court of Appeal disagreed, and disagreed firmly enough to overturn that decade old obiter guidance entirely.

The court held that the second gateway requires the original claim and the proposed new claim to be the same claim in substance. A claim that BDB Pitmans is liable for Pitmans' negligence, based on an alleged transfer of liability, is not the same claim as one alleging that Pitmans is liable for its own negligence directly. The core facts needed to establish liability are different. One claim turns on whether a transfer of liability took place. The other turns on whether the original advice was negligent at all. Swapping the defendant here would not continue the same action against a different name. It would substitute an entirely different claim, built on different facts, against a different party.

Because that changes an essential element of the original claim, the second gateway was not satisfied either. The substitution was refused, and the claim against the true wrongdoer was, in effect, time barred.

For defendants, particularly firms that have been through mergers or rebrands, this is a significant tightening of protection. Claimants can no longer rely on a generous reading of the second gateway to resurrect a claim against the right party once limitation has passed, simply because they can show the claim is connected to the same underlying facts. The claim has to be the same claim, not merely a related one.

For claimants and their advisers, the lesson is blunt. If a firm has merged, renamed, or restructured, do not assume you know who inherited its liabilities. Identify the correct legal entity that gave the advice, and if there is any doubt about a successor firm's liability, issue protectively against both before limitation runs out. Waiting to work out the corporate structure afterwards is not a strategy the courts will now rescue you from.

You might never work in professional negligence, but this case is a gift for interviews and assessment centres for one simple reason: it shows you understand the difference between procedure and substance, and why that distinction has teeth.

It is also a genuinely good story about why corporate structuring matters beyond the transaction itself. Mergers and rebrands are not just a commercial event for the firms involved. They create real uncertainty for anyone who might later need to sue them, and this case shows that the courts will not always smooth that uncertainty over on a claimant's behalf.

Permission to appeal to the Supreme Court was granted "as of right" in February 2026, which tells you how significant the profession considers this issue to be. Until that appeal is heard, the Court of Appeal's answer stands: a mistaken belief about who inherited a firm's liabilities is not the same as a mistake about a firm's name, and substituting the true wrongdoer after limitation has expired will only be allowed where the claim against them is, in substance, the very same claim. Get the entity wrong, and the door may already be closed before you realise you knocked on the wrong one.

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