But Robert Jenrick this week opened the door to a comeback for Mr Johnson, with the Tory leadership candidate saying he would be “delighted” to welcome his former boss back as an MP.

Mr Jenrick also indicated he would be “delighted” if Mr Johnson were to return to Cabinet.

However, Sir Jacob Rees-Mogg, speaking to Johnson’s father Stanley on GB News’ State of the Nation programme, said a future Conservative Party leader could now bring the ex-PM back, even without a seat in parliament.

The Constitution generally assumes that Prime Ministers must be Members of Parliament. However, Sir Jacob agreed with Stanley Johnson that this rule does not always apply.

For example, Alec Douglas-Home was briefly Prime Minister in the 1960s while standing for the House of Commons.

Sir Jacob said there were even fewer constitutional restrictions on non-MPs serving in the shadow cabinet, particularly for a position as chairman of the Conservative Party.

He added: “If Robert Jenrick wanted to appoint Boris as chairman of the Conservative Party and Boris was prepared to do that, there would be absolutely nothing that could stop that.”

Since leaving the top of politics, Johnson has earned millions of pounds from speaking engagements around the world.

Earlier this week he was also spotted on holiday in Greece, where he wore a T-shirt with a possibly cryptic message for former Prime Minister David Cameron.