British banking regulators are investigating whether a prominent conservative has been blacklisted by banks there, perhaps because he is what banking regulators call a “politically exposed person.”

A former leader of the U.K. Independence Party now working as a commentator on the conservative GB News channel, Nigel Farage, has been on a crusade in recent days against what he calls a “de-banking madness” that led to both his personal and business accounts being closed by a prominent British bank, Coutts & Co.

In a six-minute video posted on social media June 29, Mr. Farage said a bank left unnamed at the time had informed him that it was closing his accounts and that several other banks had rejected his attempts to open new accounts to replace them. He said that the move amounted to political persecution for his support of the Brexit movement and that “the establishment” was trying to force him out of the United Kingdom.

“Without a bank account, you effectively become a non-person. You don’t actually exist,” he says in the video. “It’s like the worst regimes of the mid-20th century, be they in Russia or Germany. You literally become a non-person.

“I’m beginning to think that perhaps life in the United Kingdom is now becoming completely unlivable because of the levels of prejudice against me,” he adds. 

After several days of press coverage of Mr. Farage’s complaints, the U.K.’s equivalent of the treasury secretary, Chancellor Jeremy Hunt, asked a city commissioner, Andrew Griffith, to investigate the complaints about “de-banking” by Mr. Farage and other high-profile conservatives, according to the Financial Times.

“Banks and payment providers occupy a privileged place in society, and it would be a concern if financial services were being denied to those exercising the right to lawful free speech,” Mr. Griffith told the newspaper.

Coutts bank, founded in 1692 and one of the oldest banks in the world, is a private bank based at London preferred by Britain’s nobility. It is often referred to as “the Queen’s bank” because the royal family has been a client since George IV reigned and is considered one of the most exclusive banks in the world because being accepted as a client requires significant net worth and liquid assets.

Since Mr. Farage accused the bank of giving him the boot, it has told press outlets in the U.K. that it closed his accounts because he no longer met the required minimum balance threshold. The bank requires customers to have a savings account balance of at least 3 million pounds sterling, or about $3.8 million at current exchange rates, or borrow or invest 1 million pounds at the bank. 

Since then, though, other customers of the bank have stepped forward to claim that they have accounts below those thresholds that have not been closed. Mr. Farage claims that he has held the account for more than 10 years, and at no point was he informed that his balances fell below any required thresholds.

“I have been with them for a decade and at the moment I have more money sitting on current account than I have had for most of that time,” he told the BBC, using the British term for what Americans would call a checking account.

Mr. Farage believes that he is being persecuted for his political beliefs and that the bankers are using a cudgel that applies to what the European Union and U.K. banking regulators call “politically exposed persons.” Politicians who fall into the category of politically exposed persons are subject to tighter controls, especially if a source of their funds originates overseas. Mr. Farage says he has been unfairly tarred with the title because he received money from Russia at one point for appearances on the Russia Today television network. 

Some members of the Conservative Party have rallied around Mr. Farage, turning his crusade into a debate over free speech and controversial viewpoints. Members of parliament have said he is one of a number of people who have had their lives “wrecked” by the PEP label.

Parliamentarian Tom Tugendhat, speaking in the House of Commons Monday, said it should be “completely unacceptable” for banks to close accounts for political reasons if that is indeed what is happening.

“PEP is there to prevent the corrupt use of banking facilities by politicians in corrupt regimes,” Mr. Tugendhat said. “It is not here to silence individuals who may hold views with which we may or may not agree.

“Such a closure on political grounds, if that is indeed what has happened — after all, we have only the allegation of it at this point — should, therefore, be completely unacceptable.”