He has the cheerful, inoffensive look of the ageing star of a boy-band. He wants to destroy the institutions of the French state but cultivates, brilliantly, the image of a concerned, plain-talking, working-class boy-next-door. He has become the second most popular political figure in France, after President Nicolas Sarkozy.

The baby-faced postman and Trotskyist idol of the young, Olivier Besancenot, 34, will launch this weekend something which has been, until now, a contradiction in terms: a mass-appeal, far-left party. The Ligue Communiste Revolutionnaire (LCR) is dead. Long live the Nouveau Parti Anti-Capitaliste (NPA).

The party, which plans to build a non-capitalist state and is looking, first of all, for a catchier name, will be founded during a three-day conference starting on Friday at Saint Denis, just north of Paris. With the world’s financial system in crisis and with bankers universally loathed, with the working class restless and the French parties of the centre-left rudderless and divided, there could hardly be a better time to launch a radical new movement of the left.

M. Besancenot’s old party, despite its workerist rhetoric, was mostly middle-aged and middle class [not really...]. The new party to be born this weekend will be younger and will include some working-class, trade union activists but will be dominated by the “lost” generations of French middle-class youth who reject middle-class ideas – extreme ecologists, feminists and anti-globalists, people who are fiercely in favour of illegal immigrants or fiercely opposed to advertising.

The NPA already claims almost 9,000 members. This is three times as many as the outgoing LCR, the most powerful of the many French Trotskyist groups, which will “dissolve itself” tomorrow to provide the organisational structure and the leader of the new party.

Above all, the leader. The NPA – or whatever it finally calls itself – is unashamedly a vehicle for the personality and communication skills of the LCR’s “spokesman” M. Besancenot. Le petit facteur (the little postman) with the clean-cut looks and jargon-free language was the political revelation of the 2002 and 2007 presidential elections.

In 2007, he won, with 4.1 per cent of the vote in the first round, an election-within-the-election on the left-of-the-left, crushing the once powerful Parti Communiste and two Trotskyist rivals. He is now credited by pollsters with up to 18 per cent of voting preferences – something unheard of for the far left, even in France.

M. Besancenot is in effect, engaged in a kind of political ju-jitsu: trying to overturn the modern, Western world by using the personality and media-driven politics that he and his supporters profess to detest. He is accepted by most French people as a sincere, cheerful working-class boy, a postman with a cause – a kind of “feelgood facteur”.

This approach is not entirely popular with some diehard Trots in the old LCR, who accuse M. Besancenot of abandoning serious political “struggle” for a dangerous, careerist escapade. M. Besancenot’s rise also terrifies the traditional left-wing “parties of government”, the Parti Socialiste and Parti Communiste.

He intrigues and amuses – or once amused – President Sarkozy, who sees him as a kind of Jean-Marie Le Pen of the far left. In other words, M. Besancenot could split, rather than crystallise, the opposition to Sarkozyism and make moderate centre-left politics unworkable for years to come.

As the swell of recessionary anger grows, the President, and the French right, are beginning to regard M. Besancenot with less affection. Right-wing internet sites have been full in recent weeks of allegations that M. Besancenot is a fake-proletarian, who has a wealthy wife and secretly lives a luxurious lifestyle.

Most of these allegations are distorted or untrue. M. Besancenot does not have a wealthy wife and does not live in a posh apartment. In a broader sense, the claims do have some truth.

Olivier Besancenot is a self-made proletarian. He was born into a middle class family in the Hauts-de-Seine, just west of Paris, which was also the childhood home of Nicolas Sarkozy. His father is a physics teacher and his mother is a school psychologist. He has a degree in history from the University of Nanterre.

He became a postman in 1997 (a clever choice for a proletarian career; everyone loves a postman). He still works part-time for La Poste, delivering mail by bicycle three days a week in Neuilly-sur-Seine, just west of Paris. Neuilly, ironically, is the wealthiest and most right-wing town in France. Its former mayor is President Sarkozy.

M. Besancenot is married to a successful, but not especially wealthy, publishing executive. They have one small child. He plays football in his spare time and loves rap music (which has replaced the L’Internationale and other traditional songs of “struggle” at his public meetings).

He is never seen in the old far-left uniform of leather jacket or shapeless jumper and beard. He defies the Trotskyist stereotype epitomised by Arlette Laguiller, the perpetual presidential candidate of the other principal far-left movement, the sect-like Lutte Ouvrière. M. Besancenot wears well-fitting jeans and a black or white T-shirt. His hair is always short.

Before the 2002 presidential election, M. Besancenot was almost unknown, an assistant to the co-founder of the LCR, Alain Krivine. Since M. Krivine has been part of the French political landscape since the May 1968 student revolt, it was long assumed that M. Besancenot was just a pretty face and front man.

Careful watchers of the far left in France now believe that M. Besancenot has become not only the figure-head of the new movement but its principal driving force and strategist.

What does the new party stand for? The choice of a bland “provisional” name is significant. The words “communist” or “revolution” were excluded as “old-fashioned” and off-putting to the one-cause radicals that the new party wants to attract.

The NPA website also tells a tale. There is nothing to explain in Trotskyist detail what the ideology of the party is. Instead, the site lists dozens of approved causes, from anti-nuclear to pro-Palestine.

M. Besancenot says that the party is democratic but wants to overturn “pseudo-democratic” institutions and give people control of their own lives. This means getting rid of the market economy, starting with the nationalisation of the banks into a single “state banking service”.

Asked this week if he is still a “revolutionary”, M. Besancenot said: “More than ever. We want our ideas to govern, but not through the present institutions.”

Asked if he is a “Trotskyist” (an allegiance which he has not claimed publicly for several years), he said: “Our political logic is to take the best of the different traditions of the working-class movement, whether it be Trotskyism, Socialism, Communism, libertarianism, Guevarism, or radical environmentalism.”

This scattergun approach has been contested by a minority within the LCR, distressed at seeing their political movement dissolved overnight. Christian Picquet, the leader of the rebels, argues that M. Besancenot should try instead to create a coalition of all the disparate parties of the far left.

By merging the LCR in a new movement open to all “anonymous” members of freelance radical causes, he argues, M. Besancenot is helping to “de-politicise” public life and blurring the pure lines of ideological allegiance: something that Nicolas Sarkozy has also been accused of.

In the best traditions of Trotskyist life, the rebellious M. Picquet has been dismissed from the leadership role that he had held in the LCR for two decades.

But what if he is wrong? What if M. Besancenot has merely invented a new form of Trotskyist “entryism”? Trotskyist “entryists”, or moles, disguised themselves as moderate members of mainstream parties. M. Besancenot is, arguably, trying to create a kind of “political entryism by an entire party”. He has cleverly re-packaged radical politics for a disaffected, but non-ideological, age.