Francois Hollande
© Antoine Antoniol/Getty ImagesPresident Hollande went out of his way to insist that Britain’s defection would not shake France’s intent to “punish” President Assad

President Hollande has pledged French resolve to join a strike on Syria, putting his country in the historically rare posture of military alliance with the US in the face of British refusal.

The left-wing President went out of his way to insist that Britain's defection would not shake France's intent to "punish" President Assad. "It is ready," he said of the French military, adding that action could start before Wednesday. "The decision of the British Parliament changes nothing for our determination to act," the Élysée Palace said.

The President, who commands dozens of French cruise missiles around the eastern Mediterranean, said that France was among the few nations capable of "inflicting a sanction by the appropriate means". He said: "The chemical massacre of Damascus cannot remain unpunished."

His staff said that strikes would be ordered only if UN inspectors confirmed Mr Assad's use of chemical weapons.

After appearing to be backing away from military involvement earlier in the week, Mr Hollande said for the first time that France was ready to act without UN approval.

His martial tones masked queasiness within in his Administration. Ministers are aware that France would be more exposed as the sole serious partner of the US in an attack on an Arab state.

France is aware of the irony now in play. A decade after the French were depicted as the "cheese-eating surrender monkeys" for refusing to back the Iraq invasion, the country is is now gung-ho.

"Aren't the British strange?" said Dominique Moisi, a senior adviser at the French Institute for International Relations. "In 2003 they rush to war in Iraq alongside George W. Bush when no one had been able to prove conclusively that Saddam Hussein's regime still had chemical or biological weapons. In 2013 it is clear to everyone, even the newly elected Iranian President Rohani, that chemical weapons have been used against civilians and the House of Commons humiliates David Cameron with a negative vote." In Paris there was "an undeniable sense of self-righteousness", at the turn of events.

Mr Moisi cited three reasons why the outcome was unsurprising. France had a strong interventionist tradition, such as its drive against al-Qaeda in Mali; it had historical ties with the Levant; and as commander-in-chief, unlike Mr Cameron, Mr Hollance did not need parliamentary approval.

Only about 40 per cent of voters back French involvement, although 55 per cent favour the principle of a US-led strike on Syria.

Some diplomats cited the last precedent for the present position as the Napoleonic wars, in which the US sided with France and suffered a British attack on Washington in 1812.