British Prime Minister Theresa May takes to the stage to deliver a speech to about Brexit on the first day of the Conservative Party Conference 2016 at the ICC Birmingham on October 2, 2016 in Birmingham, England.

A deal giving London, the world's largest centre of international finance, basic access to European Union financial markets after Brexit is nearly done, a British official said.

Such a deal would give the United Kingdom a level of access to the EU similar to that of major U.S. and Japanese firms, while however tying it to many EU finance rules for years to come.

"We are making progress," the official, who spoke on condition of anonymity, told Reuters.

But the official said the financial services deal would be based around the EU's existing "equivalence" system - far short of the deep and preferential post-Brexit market access that many have been hoping for.

Another British official also speaking on condition of anonymity said that, while there was progress, nothing was finalised yet.

However, European Union negotiator Michel Barnier took tweeted on Thursday that the press article on Brexit and financial service was "misleading."

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The financial services deal was part of the overall Brexit deal that Prime Minister Theresa May hopes to strike by the end of the year at the latest, the second official said.

Britain's Brexit ministry said progress was being made on reaching a financial services deal, while the European Commission had no immediate comment.

Many top bankers fear that Brexit will slowly undermine London's pre-eminent position as the world's biggest international financial centre, and a Reuters survey found that, so far, just over 600 are moving away.

Global banks have already reorganised some operations ahead of Britain's departure from the European Union, due on March 29.

The Times newspaper reported that a tentative deal had been reached on all aspects of a future partnership on services, as well as the exchange of data.

The pound jumped following the report in The Times, extending gains in early trade to reach $1.2914 by 0855 GMT.

Britain is currently home to the world's largest number of banks and hosts the largest commercial insurance market.

About six trillion euros ($6.82 trillion) or 37 percent, of Europe's financial assets are managed in the UK capital, almost twice the amount of its nearest rival, Paris.

In addition, London dominates Europe's 5.2 trillion euro investment banking industry. While New York is by some measures bigger, it is more centred on American markets.