Britain’s military effort in Helmand has suffered many setbacks in the three years since UK forces were first deployed there. This week, however, marks the lowest point yet in the nation’s Afghan campaign. On Wednesday, five British soldiers were killed by a rogue Afghan policemen who they had been mentoring in good faith. The same day, Kim Howells, a respected Labour figure, called for UK troops to come home. All this has come on top of the debacle over the Afghan elections, with Hamid Karzai this week re-apppointed as president in a process that was manifestly flawed.

Gordon Brown has again tried to contain public unease over the war, in which 93 British soldiers have been killed this year. The arguments in his speech on Friday on Afghanistan are sound. He insisted that the biggest domestic threat to the UK comes from the mountains of Pakistan and Afghanistan – and that Britain cannot resile from “the first line of defence”. He said the core task of mentoring the Afghan national army must continue, despite this week’s horrific shootings. Above all, he made the most forthright demand yet by any western leader for Mr Karzai to root out corrupt practice and improve governance. As Mr Brown put it, there is no way that UK troops can go on dying in the name of a civilian partner that “has become a byword for corruption”.