Sir Keir Starmer has sought to play down an incident after Prime Minister’s Questions in which he reportedly had a “heated” confrontation with Boris Johnson.

The Labour Party leader said “nothing” happened after the pair left the House of Commons following a terse exchange across the despatch boxes on Wednesday.

After the session, Sir Keir had to apologise for denying having previously supported the UK remaining a member of the European Medicines Agency (EMA) after Brexit.

Mr Johnson and Sir Keir were seen walking out of the Commons together following their PMQs clash and continued their conversation while standing just outside the chamber.

According to eyewitnesses quoted by the Sun, the political rivals were seen having a “heated discussion” about the Prime Minister’s EMA remarks, allegedly resulting in Sir Keir being “led away” by ally and Labour whip Chris Matheson.

Asked by broadcasters what was said during Wednesday’s conversation, Sir Keir said: “Oh, nothing, we had a discussion on the way out.”

Pressed on whether it became heated, he replied: “No, no, no, no – we were discussing it as we went out, that’s not unusual.”

Chester MP Mr Matheson had previously called the eyewitnesses’ claims “absolute bollocks”, adding: “There was a brief chat and then Keir and I left together. Nothing more to it than that.”

Sir Keir repeated his apology for questioning the truth of Mr Johnson’s statement that the Opposition leader had previously said it would be better for the UK to remain a member of the European Union’s medicines regulator.

The former director of public prosecutions had said Mr Johnson was talking “complete nonsense” after the Conservative Party leader accused him of repeatedly calling for the UK to stay in the EMA, suggesting such a move would have hampered the country’s Covid-19 vaccine rollout.

Sir Keir apologised for the error after it was pointed out that Hansard, the official record of Parliament, had recorded him in January 2017 questioning why the UK would want to leave the EMA and that it should be something retained as part of the Brexit process.

“I had misheard what the Prime Minister was putting to me, I was wrong about that and, as I say, hands up, I got it wrong. Better to say that and just be straight about it,” he told broadcasters during his visit to a vaccination centre at an Asda supermarket in Watford.