London's dominance of the derivatives market is under threat,with European firms at risk of being blocked from usingclearinghouses in London within six months.

Industry groups fear that contingency measures already acceptedby Brussels officials to grant access until the end of March 2020don't defuse the threat posed if the political storm inWestminster pushes the U.K. out of the bloc without a deal onOct. 31. At risk are derivatives contracts with a notional value ofas much as 60 trillion pounds (US$74 trillion).

"We again find the relief ending next spring with no solutionfor continued access," Walt Lukken, chief executive officer of theFIA, which represents banks, brokers, and other firms in thederivatives markets, said in Frankfurt on Tuesday. "These measuresare critical because we don't want this regulatory uncertainty toexacerbate the market volatility that may come with Britain leavingthe EU."