The leader of Ukip, Nigel Farage MEP, must have groaned when he learned that the French National Front is now modelling itself on his party. Marine Le Pen, who is poised to take over leadership of the Front National (FN) from her father, Jean-Marie Le Pen, describes it as a “patriotic” party that has more in common with Ukip than the BNP. Given the sinister resonances that the words “National Front” have in Britain, Miss Le Pen has presented Ukip’s opponents with a seasonal gift. “Ukip – backed by the French National Front” is a rhetorical swipe worthy of David Cameron’s description of the party’s supporters as “fruitcakes, loonies and closet racists”.

We should not, however, be too quick to dismiss reports that a sanitised Front National has succeeded in reaching out to a new constituency. The FN’s selling point is its opposition to the “Islamisation” of French public life – but not, it is careful to add, to Islam itself. Miss Le Pen claims that pork is being taken off the menu in French schools and that state funds are being used to build “ostentatious mosque cathedrals”. She may never be elected president, but over a quarter of French voters approve of her; at no point in the history of the Fifth Republic has an aggressive Right-wing party enjoyed such support among the middle classes.

It may seem inconceivable that British politics could move in the same direction. But we should not be too relaxed about the fact that populist Right-wing parties have never broken into the mainstream of our politics. Two points need to be made.

First, that Muslims have migrated to Britain in enormous numbers over the past 40 years; one of the heaviest waves of immigration was encouraged by the last government. The Pew Forum on Religion and Public Life estimates that there are 2,869,000 Muslims in Britain, an increase of 74 per cent on its previous figure of 1,647,000, which was based on the 2001 census. No demographic statistics are reliable in an era of open borders, but such an expansion is unprecedented.

The second point is that – different political traditions notwithstanding – Britain is beginning to experience French-style anxiety about Islamisation. The fact that many terrorists are Muslims may lead to unfair assumptions about the loyalty of British Muslims. But, at a time when – according to some surveys – around 40 per cent of the Muslim community support the establishment of Sharia, fears of social fracture are understandable. Meanwhile, government attempts to ease tension by empowering to unelected “community leaders” have caused huge resentment. It is worth noting that the Oldham and Saddleworth by-election next month was caused by the disqualification of a Labour MP caught stirring up anti-Muslim sentiment.

These tensions must not be allowed to grow, especially when collapsing party allegiances could create space for Right-wing populism. Responsible politicians must accomplish a difficult double manoeuvre. On the one hand, they should resist the anti-Muslim dog whistle that Phil Woolas allowed to be blown on his behalf. The Front National is not an appropriate model for a political party in a country whose heritage, unlike that of France, is explicitly Christian and tolerant. We trust that Mr Farage will repel Miss Le Pen’s advances. On the other hand, the Government needs to start dismantling an Islamisation that threatens the freedoms of ordinary Britons – including Muslims who are confined to ghettos that can be difficult to leave, especially for women.

In the long run, halting this erosion of freedom may prove just as important a challenge for the Coalition as easing the pain of cuts. Few subjects are more difficult to discuss without causing offence. Even so, this particular conversation is long overdue.