But UK Finance chairman Bob Wigley told Sky News' Ian King he did not believe accounts were being closed on political grounds.

He said: "Our members would say, all of them, no one should ever have a bank account shut because they express a legally held opinion but I don't believe that is what is happening," Bob Wigley said.

Instead, he added, closures will have been for other reasons.

"I'm not commenting on any particular individual here, I hasten to add, it may be because of suspicious activity in the account because as you know we're regulated and have to look at it," Mr Wigley said.

"It may be because of abusive behaviour in branches, it could be a whole host of reasons but it will never be because someone expresses a political opinion if it's legally held".

It comes as the Financial Conduct Authority (FCA) has been asked to speed up its examination of banks' treatment of so-called "politically exposed persons" (PEPs), people who have held a high-profile public role, such as political office.

City minister Andrew Griffith wrote to the regulator on Tuesday making the request, adding that, "some financial institutions may be failing to strike the right balance of taking a proportionate approach based on a careful evaluation of the actual risk".

The FCA's executive director for competition, Sheldon Mills, said of the issue today: "This is a democratic society. Your political views are your own. Where one needs to think about in terms of any service provision is how that engagement is between the customer and institution.

"And banks also have colleagues who they need to, who they employ and who they protect."

PEPs require increased oversight by financial institutions as they are at greater risk of being bribed due to the nature of their work.

Former member of the European Parliament and leader of Ukip, Nigel Farage, this week said his account had been closed because he was a PEP.

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Nigel Farage's bank accounts: What's it all about, and what's the Coutts threshold?

It was reported the account was with Coutts wealth management, and that it was closed because he did not meet their wealth threshold, which requires customers to borrow or invest at least £1m or deposit £3m in savings at the bank.

Correspondence seen by Sky News shows Metro Bank would not open an account for an anti-transgender group.

"Our policy doesn't currently allow organisations to receive donations if not a registered charity, and for community groups to be linked to, or influence political policies or legislations," the bank rejection letter said.

When approached for comment Metro Bank said, "We cannot comment on individual accounts."

"Any decision not to open an account will be based on a variety of reasons such as, commercial, legal and regulatory factors (including money laundering), and is not based on the personal or political beliefs of the individual or organisation."