In a paper for discussion forum Politeia, leading City lawyer Barney Reynolds of Shearman & Sterling has also suggested that if the UK is forced to leave the EU without a deal it could be better for the City than if it signs an agreement.

The report is a body blow to Remainers who have claimed through their Project Fear campaign that Brexit will be a disaster for the City and deprive the treasury in billions in revenues as financial services providers flee to Brussels and Frankfurt.

Instead, it reveals that London is secure and can prosper further outside EU control.

It also strengthens Theresa May’s hand as she approaches the crucial European Council meeting this month when the rest of the EU will decide whether or not to move on to trade talks.

If they block progress than the chances are that Britain will leave with no deal and Mrs May could end the negotiations.

The detailed analysis by Mr Reynolds shows how French President Emmanuel Macron has already failed in his attempts to attract “thousands of jobs” in the financial services from London to Paris.

Mr Reynolds notes: “Economically, the UK’s openness to global markets and competitive free trade, and London’s magnetic attraction for global capital, have also contributed to the success.

“So much so that today Britain remains one of the most stable, predictable and transparent places where the financial sector can do business and trade globally and with the EU. That will not change after Brexit.”

He pointed out that President Macron’s “eagerness to attract UK based firms” is finding that initial forecasts of thousands preparing to relocate have not materialised.

He also dismissed the claims that without EU passporting the UK will not be able to conduct its financial services in the bloc.

He said: “Fears in the sector about ending the passport have diminished as the true position becomes clear: for most cross-border transactions the passport is unnecessary.

“For the small number of activities which need it, different arrangements can be substituted with little extra cost.”

He said: “A no deal outcome is not to be feared. It is likely in the long term to have benefits which could even be as good as mutual recognition.”

He pointed out that technical legal arrangements known in the sector as “reverse solicitation” means that EU clients can continue to use UK based financial services without any arrangement in place and with Britain having no interference on its regulations.

Separately he noted that EU businesses can simply give themselves a presence in the UK, pointing out: “The other way for businesses to service EU customers entirely from within the UK is for those customers to establish small branches or offices in the UK to receive the services.”

Mr Reynolds paper is the latest part of growing evidence that Brexit will be a major boost for the British economy.

If the UK had remained in the EU then Brussels had plans in place to impose further regulations and taxes which would have undermined the success of the City of London.

The pro-Brexit group Economists for Free Trade has estimated that a “no deal” situation where Britain goes on to World Trade Organisation rules will help the UK economy grow by an estimated £135 billion a year.

Welcoming Mr Reynolds’ report, a spokesman for Economists for Free Trade said: "Barney Reynolds has correctly identifies that the UK must have an attractive Plan B.

“He has identified how financial businesses don't need to move much, if anything, to the EU-27 for the contingency of a No Deal. The UK should be optimising the environment here to ensure it remains competitive in a plan B scenario.

“Mark Carney has already made some welcome remarks about EU regulations the UK would look to drop."