PARIS (Reuters) - Britain’s exit from the European Union will potentially put London, the EU’s biggest capital market, out of reach, putting pressure on the other 27 countries to find new ways to finance their economies.

Stormy clouds surround Big Ben in Westminster, central London, Britain, June 9, 2017. REUTERS/Clodagh Kilcoyne

Britain has the EU’s biggest financial market, where companies from across the EU raise money by issuing shares or bonds, meet with institutional investors and buy and sell securities and derivatives.

But the UK is leaving the bloc in March 2019 and future trading relations between Britain and the EU have yet to be agreed. This is now raising fundamental questions over whether an EU of 27 countries should rely so heavily on a country outside the bloc to fund its economy.

The EU has already sought to reboot its plans for a Capital Markets Union or CMU to increase capital market funding for the economy, a project originally conceived with Britain inside the bloc.

This will not be enough for some.

Olivier Guersent, the European Commission’s top civil servant for financial services, said it was unlikely that any jurisdiction would accept being so heavily reliant on an outside financial centre as the EU would be on Britain after Brexit.

“This thinking needs to happen,” Guersent said on Tuesday at a conference organised by the EU’s markets watchdog ESMA.

Sylvie Matherat, chief regulatory officer at Deutsche Bank, which has a large chunk of its capital market operations in London said: “The CMU is really a wonderful idea but to make it work we need to have a market, and currently within Europe we don’t have a market.”

“The CMU is not enough post Brexit”, Rainer Riess, director general of the Federation of European Securities Exchanges, said. “We don’t have the equity buffer in our economy.”

Fabrice Demarigny, a former ESMA official, said a high level group should look at the EU capital market after Brexit, to see if it has enough critical mass to finance the region’s economy.

“We need a clear and ambitious strategic sense of direction to make sure the union will be properly equipped to finance itself,” Demarigny said.

Guersent also said the EU should let the raft of financial rules agreed since the 2007-2009 financial crisis bed down. He said if financial rules were continuously changed, long-term investment could be hit.

The EU has approved scores of new rules to make banks and markets safer and more transparent as part of an intensive global effort to improve the stability of the financial system since the crisis.

“I think we should now let the dust settle,” Guersent said. “We should not launch an all big, new workstream.”