London/Paris: Britain believes that Francois Fillon, the surprise favourite to become the next President of France, could “enhance the cause of Brexit” because he is an Anglophile who moulds himself in the image of Margaret Thatcher.

Fillon, who has a Welsh wife, surged ahead in the first round of a Republican Party contest to choose the party’s candidate for the race to become the head of state in May, forcing his former boss Nicholas Sarkozy to crash out of the race.

He has called for a “Thatcherian revolution” in France with “less state intervention” and more support for private enterprise.

If he wins the Republican nomination he will face Marine Le Pen, the leader of the anti-EU and anti-immigrant Front National.

A Whitehall source said: “When you look at his outlook and who he is, it wouldn’t be a bad thing. He’s the complete opposite end of the spectrum to de Gaulle. He’s an Anglophile, it might enhance the causes Brexit.

“The view is that he’s a very serious contender and could win quite a significant victory. He could sweep up those on the periphery of the Le Pen support and move into the sphere where Sarkozy is.”

The Government’s optimism over the relationship comes despite the fact Fillon was strongly against the UK leaving the EU before the referendum, saying that it would be “very bad news”.

Brexit, he warned before the vote, “could fuel the populism already at work in Europe. The debate mustn’t be reduced to holding referendums or not, but should help us think about the way Europe can be reformed.” He has expressed some Euroscepticism in the past — voting against the Maastricht treaty, which laid the groundwork for the creation of the euro, and breaking ranks with his party in opposing the EU constitution, which died in 2005 when French and Dutch voters vetoed it in referendums. But in a speech to parliament in June, he made it clear that Europe must not be too conciliatory with the UK, calling for Brexit to be “calm but swift”. “The aims should be clear: the English are leaving but that doesn’t mean the English should become our adversaries. Neither hostility nor complacency,” he said. However Britain may have concerns about Mr Fillon’s support for a US alliance with Vladimir Putin, the Russian president, over Syria. Britain is strongly opposed to such an alliance amid fears it will bolster the Assad regime. On migration, Mr Fillon has accused Angela Merkel of underestimating the risks from Islamist militants with her decision to allow hundreds of thousands of migrants to enter Germany last year.