LONDON Aberdeen Asset Management (ADN.L) Chief Executive Martin Gilbert said his company will have to move some jobs to Europe from Britain if the European Union insists that the clearing of euro denominated trade should be based inside the bloc.
Gilbert declined to say how many jobs would have to move, but told a financial conference on Thursday it would probably be a "handful".
The EU's executive will next month publish a draft law on how clearing of euro denominated securities - an activity currently dominated by London - should be handled after Brexit.
The options include insisting on direct scrutiny of clearing houses outside the bloc, such as in London after March 2019, and even requiring clearing to take place inside the euro zone.
The chairman of BNY Mellon's European operations Michael Cole-Fontayn said customers will face higher costs if London's financial markets lose access to the single market.
He said the banks based in Britain currently provide 180 billion euros of lending to EU companies and countries and they help support about 1 trillion euros of trading activities.
"Ultimately, it is going to be the end client who is going to bear the impact of a lower level of liquidity and the potential for higher costs," he said.
"These costs are pretty enormous."
(Reporting by Andrew MacAskill and Huw Jones; editing by Alexander Smith)