“Uncontrolled” immigration from the European Union is driving down wages and putting pressure on schools and the NHS, Boris Johnson has claimed during a tense exchange with MPs on the potential impacts of Brexit.

The Mayor of London, the figurehead of the Leave campaign, who has previously been an outspoken advocate of immigration as a driver of economic growth, said that it was “absolutely wrong” that Britain did not have the power to “control these flows”.

In a marathon session in front of the House of Commons Treasury Committee, Mr Johnson also claimed that membership of the EU could undermine UK security, citing border control and European Court of Justice rulings blocking surveillance of potential terrorists’ mobile phone data, warning that such decisions pointed to an economic union that was “morphing into a political union of the kind that I think is no longer in our interests”.

He said that controlling immigration would also be good for low income workers.

“The London economy along with the rest of the UK economy would benefit from the removal of a huge amount of regulation and red tape,” he said. “It would also benefit many, many Londoners on low incomes who currently have very poor access to services such as the NHS, or education or whatever it happens to be, simply because of the pressure on those services from uncontrolled immigration.

“I must be very honest about this. I am pro-immigration, I think it’s a good thing, but it is absolutely wrong of politicians to be unable to control those flows.”

Boris balloon blunder

James McGrory, chief campaign spokesman for Britain Stronger In Europe, said Mr Johnson’s position was “based on political expediency”.

“He has previously been a vocal advocate of freedom of movement, further enlargement of the EU and warned against lower immigration. This is opportunism of the worst kind,” Mr McGrory said.

Mr Johnson was also taken to task for previous claims about the EU, which the committee’s Conservative chair, Andrew Tyrie, said took “exaggeration to the point of misrepresentation”.

Mr Tyrie, who has not yet declared which side he will back in the referendum, challenged Mr Johnson over recent claims that EU rules included such edicts as a ban on teabag recycling and that children under eight cannot blow up balloons.