Barclays, JP Morgan, RBS, UBS and Citigroup are being sued by investors over allegations they rigged the global foreign exchange market, in a test of US-style class actions in Britain.

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The claim, estimated to be worth more than 1 billion pounds ($1.24 billion), was filed at the Competition Appeal Tribunal (CAT) on Monday, US law firm Scott & Scott said.

JP Morgan, RBS and UBS declined to comment. Barclays and Citigroup did not immediately respond to requests for comment.

Some of the world's biggest investment banks have already paid more than a combined $11 billion in fines to settle US, British and European regulatory allegations that traders rigged the currency markets.

Litigators have long hoped to replicate in Britain the success of US class action claims against banks, including Goldman Sachs, HSBC and Barclays, that have resulted in $2.3 billion in settlements for big investors.

In May the European Union fined five banks a combined 1.07 billion euros ($1.19 billion) for forex rigging through cartels of traders known as "Essex Express" and "Three-Way Banana Split".

The lawsuit is being led by Michael O'Higgins, the former chairman of British watchdog the Pensions Regulator, and is being funded by litigation finance group Therium.

O'Higgins told Reuters the total value of the claim would depend on the number of forex trades executed in London for UK-domiciled units - which will be automatically included in the action - and the proportional impact of rate-rigging on these.

Given the size of London's forex market, O'Higgins said the total value would likely exceed a billion pounds.

"Even on a relatively conservative assumption it's certainly a billion pounds and possibly several," O'Higgins said.

"Markets should be fair as well as free and in this case, the markets weren't fair."