The U.K. and U.S. sought to allay fears of disruption in the multi-trillion-dollar derivatives market, vowing to put in place emergency policies to ensure trading continues uninterrupted in the event of a no-deal Brexit.

The heads of the Bank of England (BOE), Financial Conduct Authority (FCA), and U.S. Commodity Futures Trading Commission (CFTC) promised a seamless transition after the U.K. leaves the European Union (EU), whatever form the separation takes. The agencies' moves would help traders use many key exchanges and clearinghouses, including those run by the London Stock Exchange Group Plc., CME Group Inc., and Intercontinental Exchange Inc.

The authorities said they would carry over existing agreements struck between the EU and the U.S. because those will no longer cover the U.K.'s relationship with America post-Brexit. Without an arrangement in place, trillions of dollars in swaps, futures, and other derivatives could be thrown into question at the world's biggest banks and money managers.