Lord Raglan, the British Field Marshal in the Crimean War, was standing on a hill with his ally, the French general, when they saw Russian - that is, enemy - cavalry gallop by. His Lordship, still fighting Napoleon, wheezed: "There they go, the damned French." Fifty years later - 100 years ago this week - Britain and France signed a treaty of friendship, "the Entente Cordiale", which led us to fight together in two world wars but never quite stopped us fighting each other.
A quarter of a million young French people roost in Britain, mostly in London, enjoying the jobs and dynamism that they can't find in France, while 150,000 Britons - many of them middle-class and middle-aged - live in rural France, enjoying the space, the public services and the quality of life that they can't find in Britain. And yet, to some Britons, and a large part of the British press, the words "French" and "foe" are still synonyms.
The Queen travels to Paris by Eurostar today for a three-day state visit as the first part of the centenary celebrations. President Jacques Chirac will pay a return state visit in November. The two events celebrate the "100-year peace" between the two old enemies. Cultural, sporting and population exchanges between the two countries have never been greater.
However, the Entente Cordiale was primarily a political document and, politically, Franco-British relations might appear to have reached rock bottom. Just over a year ago, the British Government accused the French of playing a selfish, devious game in their opposition to the invasion of Iraq. The French government accused the British of cravenly joining an American crusade on doubtful evidence of an immediate Iraqi threat.
At one point, the French protested officially (and accurately) that Tony Blair's Government was lying about Mr Chirac's position in order to stir up anti-French feeling and war fever in the British press and public.
So what is there to celebrate this week? Quite a lot, actually.
Since the Iraq war, Franco-British relations have returned to a remarkable level of calm, even outward warmth. Mr Blair is now a regular participant in the Paris-Berlin gatherings which used to precede all big EU occasions. The Franco-German axis has become a Franco-German-British three-wheeler.
Mr Blair's Government has pushed ahead with the Franco-British-led plans for an EU defence policy, semi-detached from Nato. Detailed plans are being negotiated for a joint Franco-British construction programme for aircraft carriers (two British and one French). An announcement is expected by next year, the 200th anniversary of Trafalgar. Maybe the French should call their ship the Nelson and we should call one of ours HMS Napoleon.
How can one explain such a seamless return to apparent friendship? Is this just the usual hypocritical gloss on an endlessly difficult - even impossible - relationship? A senior French official, who has been involved in cross-Channel, political dealings for many years, says that the truth is rather the reverse. The quarrels, which naturally take the headlines at both ends of the tunnel, tend to disguise common interests, which have, if anything, converged, in recent years.
"Quarrels come and go: the beef crisis; the Sangatte refugee camp; even Iraq. Ministers and prime ministers, also come and go. Some of them get on well. Some don't. But these are just the occasional eyesores or rapids," the senior French official said. "Beyond and beneath all of this, the river of British-French relations actually flows surprisingly strongly, more strongly than, say, 10 or 20 years ago."
Britain and France are like twin planets in the same orbit. The have roughly the same economic weight and roughly the same size of population. They are bound to agree and they are also bound to disagree, because the twin planets have developed radically different economic and political eco-systems. Even though the two countries seem to be trying to converge economically - more public investment in Britain; attempts to cut back the public sector in France - London and Paris still take diverging views within the EU on issues such as taxation and de-regulation.
The British "planet" is also much more comfortable with exposure to the great sun of American, political and cultural influence. Much of France, both on the left and the right, regards America as an affront to the French way of life (while the rest of France consumes huge quantities of Big Macs and second-rate American TV shows).
Hence, the great, political divide on Iraq. Mr Blair assumed his place was to try to influence US policy from within. Mr Chirac assumed his place was to chivvy or oppose the Americans from without. These divisive forces will not go away.
However, one significant and surprising force is bringing Britain and France together: the enlargement, and changing pattern of government, of the European Union. Traditionally, France has seen the EU as an extension of French power. Britain has tended to see the EU as as a threat to and a dilution of its own strength.
France has been more ready than Britain to accept the notion that common European policies can defend both European and national interests more effectively. The abstract notion of "Europe" is more saleable to the French, who enjoy abstract thought and grand plans, compared to the British, who prefer to muddle along. However, in recent years, attitudes towards Europe have shifted in both countries. Britain, under Mr Blair, has wanted to influence from within, rather than always fight Europe and trail in its wake. France has started to feel, and resent, the pinch of EU rules, from laws against bird-hunting and industrial subsidies to Europe-wide competition for big contracts.
Although still divided by some old favourites, such as farming, budget rebates and taxation policy, Britain and France now take a broadly similar view of how the EU should develop; what should be the scope and the limits of Brussels' power. In negotiations on the new European constitution, France and Britain disagreed in surprisingly few areas. Our "red lines" were mostly their red lines.
The main focus of this new "entente communautaire" is the drive to create an EU defence policy, in parallel with the Atlantic Alliance. Some arguments for an EU defence policy are practical but its unspoken mission is not to destroy Nato, as some fear, but to create a new core of unity within the looser, sprawling EU of 25, and eventually more, nations. That will not be a purely Franco-British core but - just as the US dominates Nato - an EU defence policy will inevitably be dominated by Britain and France, the only significant military spenders.
The Paris-Berlin axis will also survive, because it has to. But new alignments will form - already are forming - which are as much defensive as they are assertive. The enlargement to the east has convinced both the French and Germans that they can no longer direct the EU as they did. To protect their influence, they need reinforcement at the centre: hence the opening of their club to Britain.
Post-Iraq, Mr Blair has enthusiastically seized this opportunity. The Rumsfeldian - and maybe Blairist - fantasy of a "New Europe" controlled from the Polish, Spanish and British periphery has collapsed. We are stuck with the French as friends again whether we, or they, like it or not.
Francophobes, fear not. Franco-British relations are unlikely to become an untroubled idyll. That was not the case in 1854, 1904, 1914, 1940 nor 1944. Other quarrels - other beef wars, other Iraqs - will arise to fulfill our profound, psychological need for cross-Channel Punch and Judy shows. On each occasion, we can continue to exclaim, somewhat missing the point like Lord Raglan: "There they go, the damned French."Reuse content