Listening to Sarkozy's warmth for Britain is to relegate the froideur of Jacques Chirac and all French presidents since de Gaulle to another era. Giscard, Mitterrand and Chirac all paid lip service to being friends of Britain, but their distrust for "les anglo-saxons" was palpable.

Sarkozy is the first French president to use a different, warmer, tone. It reminds me of Tony Blair's address in French to the National Assembly in Paris in 1997 which I helped to write.

Blair used the phase "main dans la main" – hand-in-hand – which Sarkozy repeated twice to offer to the French a new relationship with Britain. Alas, neither Jacques Chirac nor Lionel Jospin were able to rise to the challenge in 1997.

I hope that today's generation of leaders in Britain can take M. Sarkozy at his word – or will London's traditional cynicism and distrust of Paris again rise to the surface and in a few months time France and the UK will be bickering again?

I hope not, but it needs a new tone in our political class, and in our media to turn Sarkozy's offer of a new 21st century friendship between Britain and France into concrete results.

Yet Sarkozy's warm words towards Britain, even his jocularity about football, mask the significant political difficulties that he faces back home – and how France is in need of a "soft revolution" along the lines of the reforms that Tony Blair successfully delivered here in Britain.

On a recent visit to Paris, I was shocked at the number of homeless people sleeping in the cold and rain in doorways of the richest arrondissements.

Leave the Gare du Nord where the new Eurostar train sweeps in after its two-hour trip from London and you have to thread your way over beggars and the homeless, victims of the French indifference to expanding their economy.

Indeed, the crisis in France can be summed up simply: a quarter century ago, the French economy was 15 per cent bigger than Britain's and growing faster.

Today, the French economy is 10 per cent smaller than Britain's and is slowing down – again. Some 400,000 of France's best business brains work in Britain. Some 400,000 of France's best scientific and technological minds work in the United States. Yet no one in France seems to question why their country drives so much of its best talent into exile.

Few answers are forthcoming either. When he took office last year, President Sarkozy promised a radiant new dawn for a confident, modernised France.

So far he is not delivering. He appears to want an economic revolution without pain. On foreign affairs, his forays with Colonel Gaddafi, his refusal to stand up to Putin's new bullying Russia and his bellicose rhetoric on Iran look curiously dated as America prepares to say goodbye to the Bush era and the world looks for new joined-up thinking on global policy.

Meantime, he has little interest or vision for Europe. His attacks on the European Central Bank, his plea for the EU to adopt protectionist economic thinking and his Islamaphobic hostility to Turkey are not far from some of the Eurosceptic nationalist thinking of Labour in the 1980s or the Tories today.

After 10 months in power, Sarkozy's poll ratings have dropped faster than any president of France since de Gaulle inaugurated the fifth republic 60 years ago. The Socialists enjoyed a tsunami of votes in the important elections for French cities and towns earlier this month. No president has come in offering so much and delivering so little.

In short, Sarkozy may be much more of an interim figure than a new de Gaulle or even a Mitterrand. He may be more like Ted Heath than Britain's Thatcher or Blair.

Heath inherited a declining Britain and thought the answer was to try and fudge his way to compromises between capital and labour. In the end, Heath alienated society while simultaneously failing to unleash new economic energy.

He wanted to reform, but like Sarkozy was not willing to be sufficiently radical to make it work.

Now, much depends on whether the French Left and especially the Socialist Party will yield to the populist temptation of hurling darts at Sarkozy's policies, without admitting that much of Left thinking and practice in the last 20 years has been part of the French problem, not a solution.

Sarkozy's state visit is a way of telling France that modern Britain is a better example to follow than a belief in the old nostrums of Gaullist nationalism or Leftist statism. But his warm words for us and his willingness to join Gordon Brown and the next US president in a new Euroatlantic alliance will only become reality if France becomes an economic power again.

A weak France cannot deliver a strong president with global ambitions. Yet, in the end, France remains Europe's indispensable nation. An unhappy France, a France without confidence in its economics, its foreign policy and its culture, drags Europe into the same uncertain state of not knowing how to interpret and change the 21st-century political-economic-social paradigms.

And those gentlemen in England so snooty and superior as they watch France struggle and suffer should park their complacency.

Whether under Sarkozy or, more probably, under an intelligent reinvented Centre Left, France will be back. And not a moment too soon.

Denis MacShane is Labour MP for Rotherham, a former Minister for Europe and author of a biography of François Mitterrand. He has been commenting for French TV and radio on Nicolas Sarkozy's state visit.