Nigel Farage has warned new French Prime Minister and “EU fanatic” Michel Barnier will suit “sell out Starmer”.

President Macron appointed the former Brexit negotiator in a bid to unify French politics.

Known in France as Monsieur Brexit, Mr Barnier will be France’s oldest prime minister since the Fifth Republic came into being in 1958.

He is set to succeed Gabriel Attal, France’s youngest ever prime minister, who President Macron first appointed prime minister in early 2024 and who has stayed in post as caretaker since July.

But Brexiteers warned Mr Barnier’s appointment could lead to a disastrous new era of relations between Britain and the EU.

They warned the senior politician is “no friend” of the UK and would be willing to pull the UK back into the EU’s orbit – if ordered to do so by Mr Macron.

Sir Keir Starmer is pushing for a reset in relations with Brussels, insisting he wants closer ties with European capitals.

Reform UK leader and Brexit architect Nigel Farage has blasted: “Michel Barnier becomes the new French Prime Minister. An EU fanatic that will suit sell-out Starmer.”

Senior Tory MP Sir John Hayes also criticised the appointment.

He said: “We thought we’d seen the last of ‘Monsieur Barnier’ after the Brexit negotiations – where he was determined to get Britain the worst possible deal.”

Sir John insisted France must “step up” and work with the UK to stem the tide of illegal migrant crossings in the Channel, urging togetherness to “stop the boats”.

Sir Jacob Rees-Mogg, a leading Brexiteer , said Barnier was “no friend of the U.K.”

“But he is a capable political operator”.

Former Tory MP Sir Bill Cash said Sir Keir “is a loose cannon on the European issue” and predicted that the new prime minister would “be able to work with Barnier — but not in the [British] national interest.”

He added: “If Macron wants that and I think he will, he wants Britain closer to the EU, that’s what Barnier will do.”

Meanwhile, former Tory leader Sir Iain Duncan Smith said it “shows the desperation of France”.

But Sir Keir’s biographer, Tom Baldwin, revealed in his book on the new Prime Minister that Mr Barnier was a fan of the Labour leader – and had even tipped him to move into Downing Street one day.

He wrote in Keir Starmer: The Biography: “Despite this veteran French politician spending most of his trying to agree a deal with the Conservative government, he also held talks with the Labour Party, writing in his diary in 2018 that Starmer was without doubt the figure in Labour’s hierarchy ‘who impresses me the most of his ability to grasp in detail what is at stake in the Brexit negotiations.

“He added ‘listening to him, I get the feeling that Keir Starmer will one day be Prime Minister.

“Starmer is clever, says Barnier. ‘What I saw over those years was how he was always learning.

“He improved, day after day, year after year. At the beginning he was wise enough to stay close to Corbyn and, while everyone else made mistakes, he was careful.

“From the first time we met I thought there was something about him.”

A statement from Mr Macron’s office announcing Mr Barnier’s appointment said he had been tasked “with forming a unifying government to serve the country and the French people”.

The statement added: “This appointment comes after an unprecedented cycle of consultations during which, in accordance with his constitutional duty, the President ensured that the prime minister and the future government would meet the conditions to be as stable as possible and give themselves the chances of uniting as broadly as possible.”

The appointment of the 73-year-old Barnier follows weeks of intense efforts by Macron and his aides to find a candidate who might be able to build loose groupings of backers in parliament and survive possible attempts by Mr Macron’s opponents to quickly topple the new government that Mr Barnier will now put together and lead.

Mr Barnier has served as French foreign, European affairs, environment and agriculture minister – and twice as a European commissioner – but until now had never had a tilt at any leadership post, like that of president or prime minister.