A British software engineer is suing the operator of BitMEX for the return of 324.8 BTC — worth about $27.2 million, or £20.4 million as of October 1 — on the grounds that the exchange traded with him in the UK without Financial Conduct Authority authorization, according to particulars of claim reviewed by Decrypt and reporting by The Guardian.

Lewis Barber filed the claim in London's Commercial Court against HDR Global Trading, the operator of the crypto derivatives exchange that shut down on September 23. His solicitors wrote to BitMEX in December 2025 rescinding the trades, the claim says. The filing has not yet been formally served.

"No such claim has been served on HDR Global Trading Limited," a BitMEX spokesperson told The Guardian.

What does the claim actually allege?

Between 2018 and 2022, Barber executed roughly 2,294 trades across five BitMEX accounts. Every one was a perpetual swap — a derivative resembling a futures contract but with no expiry date. His lawyers challenge the 1,053 trades that lost him money.

The legal theory is simple and potentially sweeping. Under the Financial Services and Markets Act 2000, contracts entered into by an unauthorized firm carrying on a regulated activity cannot be enforced against the counterparty. Barber's lawyers argue each swap was such an activity, and that BitMEX never held UK authorization — so none of the losing trades bind him.

The claim builds its case on access and marketing. It says BitMEX did not restrict access from the UK, let new users select the UK as their country of residence, and ran global promotional campaigns, including an advertisement in The Times in January 2019. It also cites an FCA warning from March 2020 stating BitMEX may have been trading regulated investments in the UK without authorization.

Barber adds a damages claim for deceit, alleging BitMEX knew it lacked authorization while implicitly representing it could lawfully trade with him.

How big could this get?

Very big, if the theory holds. Seladore Legal, Barber's firm, said in a statement that many other investors are likely in a similar position, putting the potential total exposure at hundreds of millions of pounds.

"Other UK-based persons may have entered into similar contracts with BitMEX, although whether any individual has a claim will depend on the particular facts and trading history," said Gareth Keillor, a partner at the firm.

That caveat matters. Each claimant's eligibility will turn on residency at the time of trading, account history and how the court reads FSMA's protections. A victory for Barber would nonetheless give UK retail derivatives traders a template to unwind losing positions at any offshore venue that served them without authorization — an operational and balance-sheet question for every exchange that historically welcomed British users.

BitMEX's wider legal exposure

The UK claim is not BitMEX's only live front. A proposed class action in New York alleges theft of Bitcoin and insider trading, and names co-founders Ben Delo, Arthur Hayes and Samuel Reed.

The regulatory record is already extensive. All three co-founders pleaded guilty in 2022 to violating the Bank Secrecy Act through anti-money laundering failures at the exchange. President Donald Trump pardoned them in March 2025. BitMEX itself pleaded guilty to Bank Secrecy Act violations in 2024 and a US court ordered it to pay $100 million in January 2025.

The exchange had announced its closure in July and ceased trading in September, before the UK claim landed. Co-founder Ben Delo donated £36 million to Reform UK in September — the largest single donation in British political history, as Decrypt reported.

What happens next?

The claim awaits formal service on HDR Global Trading, after which the operator must decide whether to contest the FSMA argument in the Commercial Court or seek a settlement. A ruling that unauthorized perpetual swaps are unenforceable against UK counterparties could open a claims window worth hundreds of millions of pounds across the collapsed venue — and force every offshore derivatives exchange still serving British users to reassess its legal footing.