Knives out: Boris Johnson takes on Jamie Dimon on 'Brexit'

Boris Johnson on campaign

The former London mayor rejected claims by the JPMorgan Chase CEO that the U.K.'s exit from the EU would cost jobs.

JPMorgan Chase boss Jamie Dimon has said that Britain's potential exit from the European Union (EU) could mean fewer jobs for in the U.K. Boris Johnson, a combative campaigner for a so-called Brexit, disagrees.

In an interview with CNBC, former London Mayor Johnson said that he rejected Dimon's claims about potential job losses, adding that the EU's economic policies had hurt living standards in the U.K. due to the twin effects of the euro currency and what he called "uncontrolled migration" across countries in the EU.

"Jamie Dimon and JPMorgan are the very people I recall - I mean they're bankrolling the Remain campaign - and they are the very people who urged this country to embed itself in the euro, which has turned out to be an absolute catastrophe," Johnson said in the Saturday interview.

"Yes, it is true, that some financial services institutions have over the last 20 years benefited phenomenally from the EU set-up. But it is also true that huge numbers of people on modest earnings in this country have not seen their wages rise - indeed in real terms many people have seen their wages fall as a result of many of the signature policies of the EU."

JPMorgan declined to comment on Johnson's comments.

JPMorgan's Chairman and Chief Executive Dimon said on Friday that a British exit from the EU could mean "fewer" jobs with the bank in the U.K. - where it employs 16,000 people - and more jobs in Europe, Reuters reported.

The latest comments underscored how testy the discourse had become ahead of the June 23 referendum. Support for Britain to leave the EU stood 4 points ahead of support for remaining in the 28-member bloc, according to a YouGov poll for ITV, Bloomberg reported.

Johnson's position has put him in the crosshairs of members of his own party, including Prime Minister David Cameron, who believe the U.K. should remain within the EU.

On Sunday, John Major, the former Tory prime minister, accused the Brexit camp of pushing "inaccurate and frankly untrue" information. He blasted Johnson as a "court jester" leading a campaign that was "verging on the squalid."

- Antonia Matthews contributed to this report.

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