“Of course, the prime minister isn’t a clown, he is the elected prime minister of this country with a very big mandate, leading this country through the pandemic,” he told Sky News.

The comments attributed to Macron were made privately to a small group of his advisers during a visit last week to Croatia, according to French satirical weekly Le Canard Enchaine.

The president had already lashed out publicly at Johnson, accusing him of not being “serious” in his response to the capsizing of a migrant boat in the Channel with the loss of 27 lives.

But in private he went further, according to Le Canard Enchaine, attacking the prime minister for seeking to make France a “scapegoat” for Brexit, which had proved “catastrophic” for Britain.

“Bojo [Boris Johnson] talks to me, he’s down to earth, everything’s fine, we’re having grown-up discussions, and then he sticks it to us either beforehand or afterwards in an inelegant manner,” the president is quoted as saying.

“It is very sad to see a great country, with which we could do so much, led by a clown. Johnson has the attitude of a knucklehead.”

Freeman said the use of the word “clown” was “pretty unhelpful,” but insisted the two governments are continuing to work “very closely” on the migrant issue.

“The home secretary is working closely with French counterparts on it, and the prime minister and the British government are looking for a sensible conversation with France about it,” he said.

“So, I’m confident, actually, that Anglo-French relations are rather better than that quote suggests.”

A senior government source insisted that Johnson wants good relations with France, but acknowledged they may have to wait until after next year’s presidential election for the situation to improve.

“The prime minister continues to be a staunch and public advocate for the strength of the UK-French relationship,” the source said.

“Our approach will not change, even if we have to wait until the other side of the French presidential election for a change of tone.”

Macron was particularly angry after Johnson posted a letter he had sent to the president setting out his proposals for tackling the migrant crisis on Twitter.

A French government spokesperson accused the prime minister of “double speak”, and an invitation for Home Secretary Priti Patel to attend a meeting of ministers from key European countries to discuss the crisis was withdrawn.

The latest flare-up comes after London and Paris have been publicly at odds for weeks about post-Brexit fishing rights and the Northern Ireland Protocol in Britain’s Withdrawal Agreement with the EU.

Downing Street said it was important to use “measured and appropriate language” in relation to the protocol after Macron reportedly suggested resolving the current deadlock was a matter of “war and peace”.

The president was reported to have told the European Committee of the Regions, an EU advisory body: “It’s a question of war and peace for Ireland. So we should avoid any temptation to be less than serious.”

In response, the prime minister’s official spokesperson said: “When it comes to the protocol it is vital that we use measured and appropriate language given the sensitivities involved.

“It is obviously welcome that Mr Macron recognises that a serious situation needs to be resolved. We urgently need to make progress.”