There was a time when the humanitarian crisis in Aleppo would have featured strongly in political debate in Britain. Just two weeks after a negotiated ceasefire appeared to have provided some respite, a war of attrition in Syria’s second largest city is escalating into a vast human tragedy. Last Saturday, a bomb dropped by Syrian government forces knocked out a pumping station which had been supplying water to two million people, 250,000 of whom are besieged in the rebel-held east of the city.