On Thursday, in the mountains of Bosnia, some 7,000 troops will peel off badges bearing the North Atlantic Treaty Organisation's emblem and replace them with the European Union's star-spangled insignia.

Their mission, to stabilise Bosnia-Herzegovina and hunt war criminals, will be placed under the aegis of the EU, with policy set by "security ambassadors" meeting in Brussels. British generals will take control of the forces on the ground on behalf of the EU, replacing US commanders.