Before the horrified gaze of its militants, the French Socialist party — which has been a major force in French politics since 1981, and forms the present government — is falling to pieces.

There are many reasons behind this catastrophe. They go back to 2005 and the dithering leadership of the then secretary-general, François Hollande, at a time when the party was dangerously divided after the referendum on a European constitution. And they continue up to 1 December last year, when President Hollande, after again dithering for months, announced on national television, in tears, that he had bowed to the inevitable — his own failure and unpopularity — and would not run for re-election. But the most significant reason for the Socialist implosion is the sudden arrival of a man from nowhere called Emmanuel Macron.

Macron, at 39, would normally be considered at least 15 years too young to mount a serious presidential challenge in France, but the most recent polls show him in third place, just behind the front-runner, the far-right Front National’s leader, Marine Le Pen, and François Fillon, the candidate of the conservative party, Les Républicains.

His rapid rise makes Macron a genuine original in French politics and his opponents do not know what to make of him. Unlike all other serious contenders, he has no visible record of political commitment. In 2004 he graduated from the National School of Administration (ENA) and joined the upper civil service. Then, in 2008, he paid €50,000 to buy himself out of his government contract and became an investment banker with Rothschild, where he was highly regarded and quickly made a small fortune. Then, in 2012, with the election of President Hollande, his career took another unexpected change of direction: he left Rothschild to become deputy secretary-general at the Elysée. When Manuel Valls became Hollande’s second prime minister in 2014, with instructions to deregulate the French economy, Macron was catapulted into the economics ministry.

Hollande and Valls congratulated themselves on an imaginative choice, and Macron set out to please Brussels by cutting France’s deficit while encouraging business activity. In 2015 he introduced la loi Macron, a measure designed to stimulate growth by abolishing public service monopolies and union restrictions on hours. This had to be forced through the National Assembly by decree, against the opposition of Socialist deputies, an unpopular move that consecrated Macron as the bête noire of the left.

As the months in office passed, Macron openly developed a separate political agenda, often disagreeing in public with Valls. Soon after his appointment, a mysterious movement appeared called ‘Les Jeunes avec Macron’ (‘Young people for Macron’). This was launched as a ‘spontaneous’ internet site, but quickly grew into a well-organised group numbering several thousand activists whose average age was said to be 33.

Macron then began to dominate the debate on European and welfare policy — but Hollande and Valls did nothing to rein him in. In 2015, a few days after Hollande insisted that Macron was ‘respecting his authority’, the maverick minister attacked the wealth tax — a central plank of Socialist fiscal policy since it was introduced in 1989. Meanwhile, party leaders mocked his inexperience and lack of support on the left, and estimated his electoral appeal at 6 per cent.

Undaunted, the economics minister announced that he was forming his own political ‘movement’, ‘En Marche!’ (Let’s Go!), ‘open to everyone of progressive views’ and ‘aimed at younger voters’. Last August he started touring French holiday resorts appealing for a vision that would ‘re-forge the country’s politics, culture and ideology’. At the end of the month he announced his resignation, and in November he launched the presidential campaign that he must have been secretly preparing ever since he joined the government.

While the seven hapless candidates for the Socialist party’s nomination were struggling throughout December to achieve three-figure attendance at their meetings, Macron — with no party machine behind him — was attracting thousands. In Clermont-Ferrand it was 2,500, in Lille 4,000, and in Paris last month 12,000 people packed into the hall to hear him speak.

As a presidential candidate, Macron is seen as an outsider, someone who will ‘break the system’ and challenge the stifling consensus of unions, over-entitled functionaries and remarkably youthful pensioners that prevents France from responding to the challenges of globalisation. He usually describes himself as ‘centrist’ but he also objects to being called ‘anti-socialist’.

If Macron’s unique selling point is unclear, his unique talking point is that he married his former school teacher, a lady 24 years older than him. This startling fact, when first encountered, tends to bring political discussion to a halt, while all pause for a few moments of profound reflection. His latest fan is Ségolène Royal. Ségolène is the current minister of the environment, and, by chance, she too is 24 years older than the dynamic new arrival. She has repeatedly spoken of her affection and admiration for Macron. Ségolène was the defeated Socialist presidential candidate of 2007, but last week she urged the party’s voters to ignore their own candidate, Benoît Hamon — a hardline leftist sacked as education minister by Valls in 2014 — and back Macron instead.

Macron has not just divided the Socialists, he has replaced them. So how has this apparently isolated and underfunded individual managed all this in such a short time? It is clear that Macron has powerful supporters behind the scenes, and a clue may lie in the little-discussed fact that some years ago he was identified as a member of ‘les Gracques’ — a discreet centre-left pressure group loosely staffed by influential chief executives and civil service mandarins. They are pro-market socialists who long ago gave up on the Socialist party. Many are fellow ‘énarques’ (graduates of ENA) and every step of Macron’s career could have been directed by them. Spotted as a brilliant and charming student, Macron could first have been launched into the prestigious state Finance Inspectorate, then switched into Rothschild to gain business experience (and wealthy support) and then placed like a time bomb in Hollande’s outer office, where he ticked away until he could be moved into the heart of the Valls government. Last August he finally exploded into action at the perfect moment to cause maximum damage to Hollande, Valls and the entire Socialist presidential election campaign. Macron’s rise bears all the hallmarks of a classic ENA undercover operation, a fundamental part of the énarques’ stock-in-trade and one in which the country’s leading bureaucrats are cynically trained.

Now that the Socialists have lumbered themselves with a dinosaur — Hamon — as their candidate, Macron is in an even stronger position. He will be able to tune his campaign to attract moderate Socialist voters as well as the centrists and centre-rightists who flock to his meetings and are having second thoughts about François Fillon.

Mr Fillon and his British wife Penelope are currently under investigation for misuse of public funds. Both deny the accusations. Interestingly, the information that has placed him under suspicion seems to have come from dissident members of Les Républicains, his own party — angry that neither ex--president Nicolas Sarkozy nor Alain Juppé, mayor of Bordeaux, won the nomination. If Mr Fillon is formally charged, he has said that he will not run. In which case the most likely solution for his party, at this short notice, would be to select Mr Juppé in his place.