Temporary EU permission, known as equivalence, is due to expire next March, raising the prospect of EU customers having to shift positions from London at considerable cost.

"We have a strong expectation that there will be a technical extension granted," Schwimmer told a derivatives conference.

Such an extension would probably stretch to later in 2020 by when the LSE expects to secure permanent equivalence-based access, Schwimmer said. 

(Reporting By Huw Jones, editing by Sinead Cruise)