Trading in euro rate swaps began leaving London to the European Union and United States after Britain left on Dec. 31 to leave the bloc.
EU banks could no longer sell euro swaps in London and must use a platform in the bloc or those approved by EU regulators, such as in the United States and Singapore.
OSTTRA, a new joint venture between CME Group and IHS Markit, said that in the first quarter of 2021 up to 23% of the Euro rate swaps by volume - up from 18% in the second quarter.
For UK and EU counterparties who want to trade with each other, they have little choice but to use U.S. platforms in the future.
In contrast, London's share in Euro swaps remained flat over the two quarters when the share of EU-based platforms fell from 11% to 8%, while that of the London-based platforms fell by 26%.
There has been little or no change in where swaps is cleared, OSTTRA said.
The EU is now putting pressure on banks to shift clearing of currency swaps from the London Stock Exchange's LCH unit in Frankfurt to Deutsche Boerse in London, but has met broad opposition so far.
LCH has permission to clear trades for EU clients until June next year, and Brussels has yet to say if this is extended in any form.
Bankers have warned that if permission is not extended, clearing will likely go the same way as trading with chunks shifting to the United States.
Billions of euros worth euro part trading on daily basis has also left London for the London Metropolitan Exchange and other EU financial centres, prompting Britain to review its capital market and listing rules.