It has become a cliché of defence analysis that the money we spend on overseas aid should be reduced, to find the funds for better Armed Forces. The truth is no less pertinent for its being clichéd. Equally common are stories about the lack of rigour in the monitoring of the aid budget, because all the Prime Minister seems to care about is that the money is spent. We are, therefore, in the crackpot situation of having a binding undertaking to spend a fixed percentage of the national funds on sending the wives of African despots on shopping trips to Paris and Singapore, but of having no such binding undertaking to spend a certain percentage on defence. Mr Osborne must use his speech on Wednesday to put an end to that.