Marine Le Pen and France’s would-be Trumpiste insurgents could scarcely have wished for a nicer early Easter present. Their most potent opponent, the centre-right Francois Fillon, declared with admirable insouciance that he is to be investigated for corruption – but will still remain in the race for the Elysee Palace.

Of course, Mr Fillon has been convicted of precisely nothing so far, including the allegation that he created a “fake job” on the taxpayer for his British-born spouse. But that is hardly the point. As is already the case, Mr Fillon will be distracted and under constant media pressure until the first polling day, on 23 April, and, if he gets that far, right to the decisive run-off on 7 May, when he will almost certainly be opposing the National Front’s Ms Le Pen.

Ms Le Pen will make the most of this political windfall. If she had wanted a symbol of the decadence of the French political elite she could hardly have summoned up a more vivid symbol than Francois Fillon, the former prime minister, minister and career politician.

Mr Fillon is plainly gambling on the supposed certainty that whoever makes it to the second round of the election will be able to rally moderate voters on the left and right and defeat the Le Pen charge.

Fillon announces he will not be standing down from the French presidential race

Voters, in this case of the left, will be asked to “hold their noses” and vote for the flawed Mr Fillon, to avoid the ultimate disaster of a Le Pen victory, with all that implies for French social cohesion and the future of the European project. This, after all, has happened before under the Fifth Republic; in 2002, when Jacques Chirac, a figure who was also compromised, saw off Marine Le Pen’s pere, Jean-Marie. Ms Le Pen is likely to come first in the first round, itself an indictment of the state of French society. She is also likely to do much better than her father did, perhaps 40 per cent of the vote rather than the 20 per cent or so he managed in the second round.

So Mr Fillon appears defiant and reluctant to bow out in favour of the next most credible conventional candidate, the centrist Emmanuel Macron, either before or after 23 April. If Mr Fillon does manage to beat Mr Macron then he will appeal to the French people to vote for him, warts and all, for fear of something worse. The “warts” include a policy platform reminiscent of Thatcherism, a word and a mindset that has no equivalent in the French language or culture.

Even so, Mr Fillon’s policy platform is more likely to peel away support from Marine Le Pen – even though it may also repel the traditional left, for whom abstention is a dangerously attractive alternative.

If Mr Fillon should lose out to Mr Macron for the opportunity to trounce the neo-Fascist Ms Le Pen, then it is by no means certain that Mr Macron’s undoubted charisma will be enough to persuade those on the right to put nation before ideology. It is perfectly possible that Mr Macron would stand a greater chance of losing to Ms Le Pen compared to Mr Fillon. It may be a risk that many in France would not wish to take.

Anything is preferable to rhetoric of Ms Le Pen – but will enough French voters agree? What’s more, there is also the terror that “shy” Le Pen supporters are conspiring to understate her showing in the opinion polls.

A “Popular Front” now, if that wasn’t such a heavily loaded phrase in French politics, is sometimes suggested the ideal answer to Ms Le Pen, where all the constitutional parties unite against her without delay. And yet that is in a way a denial of the normal democratic dialogue, and also merely serves to turn the presidential contest into a fight between a blob of an Establishment against the supposedly popular movement headed by Ms Le Pen. Besides, the parties just couldn’t agree.

Even if Ms Le Pen is thwarted this time, her very appearance on the ballot paper is a defeat for everything that the French republic has ever stood for. Her political influence will endure, backed by a substantial proportion of the electorate, who are choosing her and her vile policies entirely with their eyes open and with all the warnings at home and abroad ringing in their ears.

They are not being duped, in that sense, though Ms Le Pen’s programme is a fraud. They may or may not be inspired by Brexit and Trump, but they are deeply dissatisfied with what the French economy and political system is delivering for them – even though it is delivering far less for the children and grandchildren of the migrants that have become so demonised.