Britain and France to seal defence pact

British and French planes could be flying from each other's aircraft carriers before the end of the decade and tests on nuclear warheads will be conducted jointly under treaties to be drawn up today at a summit in London between David Cameron and Nicolas Sarkozy.

The treaties, which could also lead to a joint expeditionary force, are the result of months of planning by officials, encouraged by the two leaders. Unlike the original entente cordiale, which was the product of mutual concern about a hostile power before the first world war, today's is the product of hard-headed pragmatism, designed to maximise each nation's military capabilites while saving money.

Officials were given a huge boost by pressures on the British and French defence budgets, which will leave each country with just one carrier able to take aircraft. The coalition government last month gave the go-ahead to two new large carriers for the navy, but planes will be able to fly from just one – the Prince of Wales – in 10 years' time.

French Rafaele warplanes could fly from the Prince of Wales and British US-built Joint Strike Fighters could be flown from the French carrier, the Charles de Gaulle. The ships will be maintained and refitted in their home countries.

Officials said the unprecedented British-French defence and security co-operation treaty would be a decades-long commitment. As well as synchronising aircraft carrier deployments, it will pave the way to a "combined joint expeditionary force" at brigade level under a British or French commander.

The joint force would consist of troops already in each country's national armies and would only come together in the event of a crisis or emergency. Any decision to deploy the force would be taken jointly by the two governments, which would have "political control" over it, officials said.

The treaty will set up joint training for pilots – especially on the European-built A400M military transport that both countries are buying – co-operation on submarine technologies, mine counter-measures, satellite communications and air-to-air refuelling. The two countries' arms industries will co-operate on developing unmanned aerial vehicles (UAVs), and high-tech missiles as well as other weapons systems.

A separate treaty on nuclear co-operation will combine the work testing nuclear warheads conducted at the Atomic Weapons Research establishment at Aldermaston, in Berkshire, and at its French equivalent at Valduc, in Brittany. Aldermaston will concentrate on developing technology while Valduc will do the computerised testing. Britain and France have different kinds of nuclear warheads and officials emphasised that the proposed cooperation would be limited to simulated construction and safety tests which, officials noted, cost a great deal of money.

They described today's treaties as marking "a new phase of tactical co-operation between two sovereign countries". Although Britain and France already co-operated on defence, these would go far deeper and have what was described as a much "harder practical edge" than existing arrangements between the two countries. The US is said to have welcomed today's moves.