British defence contractor BAE Systems and France’s Dassault Aviation were last year awarded a contract to develop next-generation unmanned drone aircraft.

There are still sore points. Cameron has tried to persuade India to ditch a multi-billion dollar order of France’s flagship fighter jet, the Dassault-built Rafale, and instead pick the Typhoon, built by BAE and European partners.

“We cannot afford any more to have the Typhoon vs Rafale. The idea is to have one future combat air system, a Franco-British one,” said the French military source.

Experts say plans to cooperate on testing nuclear warheads in Britain and in France are on track. France has traditionally made much of its independent nuclear might, while Britain has relied in part on U.S. kit.

“Which other nations can work together on such a key element of sovereignty, opening a bit of that sanctum of a nation’s insurance policy to another?” said the French diplomatic source.

Cooperation has been hindered by timing. Britain set out its 10-year military strategy in a 2010 review, while France’s Livre Blanc is due in spring.

“There is a lack of alignment in policies between France and the UK so far. There is a gap in understanding between industries and governments,” said defence analyst Claire Chick.

FALKLANDS QUESTION

There is a limit to how far Britain can rely on French military help, Arbuthnot said, citing the example of the Falkland Islands, over which it warred with Argentina in 1982.