Boris Johnson has reiterated support for the Leave campaign's central claim that £350 million a week goes to Brussels, and said the figure is an "underestimate" of what the UK hands over.
Mr Johnson said "about half" of the money comes back from the European Union, but that cash is "under the control of EU bureaucrats".
He added that claims the key economic statement, which is painted on the side of Vote Leave's battle bus, is misleading are not true.
Mr Johnson also claimed the European Court of Justice had made "some very, very erratic judgements" banning the UK from deporting criminals, which he said was "wholly wrong".
His comments came after a senior Tory backbencher came out in favour of staying in the 28-country bloc, and branded Leave's key economic argument a "disgraceful" falsehood.
Andrew Tyrie, chairman of the influential Commons Treasury Committee, said Vote Leave's often-repeated claim that Britain hands £350 million to Brussels each week which could instead be spent on national priorities is "bogus" and should be discounted by voters.
When Mr Johnson was asked on local BBC Hereford and Worcester radio on Monday whether the figure is correct, he replied: "Well it is, and in fact that is an underestimate of the amount we give every week, or the amount we cannot control every week.
"The last figure I said was about £365 million."
He said the Leave campaign had been "clear" that "about half" the money comes back to the UK, but claimed it is the EU which dictates how that cash is spent.
Mr Johnson said: "We get money back from the EU, about half of it comes back, but that is at the behest - at the control, under the control - of EU bureaucrats."
Asked if it is a misleading claim, he added: "You are spending the money on my behalf, you're deciding what you think I should be spending that money on.
"We don't control that money anymore and a huge quantity of it is simply wasted."
Mr Johnson claimed "European officialdom" is making "many decisions" on how the UK is run.
He said: "For me that's only part of the problem, for me the real issue is the absence of control generally.
"That manifests itself in all sorts of ways, lack of control of our borders, over our security.
"The role of the European Court of Justice which has been growing so much in the last few years, which is now supreme over our entire legal system, and is now making some very, very erratic judgements."
The Tory MP for Uxbridge and South Ruislip said: "What matters to people in just 10 days' time is the future of this country and who governs this country.
"Is it going to be other European countries getting together?
"Actually if it were that simple it would be good, but it's the European officialdom that is taking so many decisions, and I mentioned the Court of Justice.
"It seems to me wholly wrong that a sovereign country should find itself in matters of security having decisions taken in that way on who we can have in this country, who we think is safe to have on our streets, by a foreign court.
"It cannot be right."
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