Britain and France today signed a landmark 50-year treaty on defence and security that envisages the joint use of aircraft carriers, a 10,000-strong joint expeditionary force and unprecedented new levels of co-operation over nuclear missiles. The deal, signed in London by David Cameron and the French president, Nicolas Sarkozy, has in part been forced on the two countries as they struggle with tightening defence budgets, but also reflects a level of mutual trust not seen for decades. At a joint press conference at Lancaster House, Cameron repeatedly stressed that the agreement strengthened British sovereignty as he said it opened a...