Caroline Nokes said the elder Mr Johnson forcefully smacked her on the backside and said she has “a lovely seat” in 2003 ahead of him running to be a Tory MP.

Mr Johnson declined to comment about her allegation made to Sky News, other than to say he has “no recollection of Caroline Nokes at all”.

The allegation prompted Ailbhe Rea, a journalist for the New Statesman magazine, to accuse Mr Johnson of having “groped” her at the 2019 Tory conference.

Stanley Johnson (right) at the Conservative Party Conference in Manchester

Ms Nokes, the chair of the Commons Women and Equalities Committee, earlier suggested that the Prime Minister’s father inappropriately touched her during the Conservative party conference in Blackpool 2003 ahead of Mr Johnson running in the Teignbridge seat in Devon in 2005.

“I’ve had male MPs stick their hands on my backside in Strangers’ Bar (in Parliament),” she said during a panel discussion.

“And I can remember a really prominent man smacking me on the backside about as hard as he could and going, ‘Oh, Romsey, you’ve got a lovely seat’.

“Stanley Johnson did that to me ahead of the ‘05 election, so it was Blackpool… 2003/4.

“I didn’t do anything and I feel ashamed by that… now I probably would.”

Responding to the allegation on Twitter, Ms Rea said: “Stanley Johnson also groped me at a party at Conservative conference in 2019.

“I am grateful to Caroline Nokes for calling out something that none of us should have to put up with, not least from the Prime Minister’s father.”

Interview: Stanley Johnson, father of London Mayor, Boris Johnson

An investigation will be carried out into allegations made against the Prime Minister’s father “if that’s the appropriate course of action”, a minister has said.

Asked about the allegations, Home Office minister Damian Hinds told Times Radio: “I don’t know obviously about the … I’ve heard this morning, as you have, or overnight, about this, about these allegations.

“I can say that, overall, in terms of the safety of women and girls, and being free from harassment wherever they are at home, at work, in the street, and online, this is an absolute top priority for the Government.

“But I’m not joining a link between that and at this because we don’t know, but if there is an investigation to be had, then, of course, that will happen.”

He added: “If there is an investigation to be had, if that is the appropriate course of action, then of course that will happen.”

Mr Johnson lost the campaign to become an MP in 2005 but had served as a Conservative member of the European Parliament between 1979 and 1984.

Mr Johnson, now 81, did not immediately respond when contacted by the PA news agency about both of the allegations.

But, regarding the initial accusation, he told Sky News: “I have no recollection of Caroline Nokes at all. But there you go … and no reply.”

Tory MP Caroline Nokes accused Stanley Johnson of groping her at the Conservative Party conference in 2003.

Stanley Johnson accused of inappropriately touching Tory MP and journalist