Nigel Morris: Commonsense policy leads into a political minefield

Politicians rarely step into the minefield of liberalising drug laws for fear of alienating the mythical voters of Middle England.

As a backbencher, David Cameron supported calls for the UN to consider legalising drugs and the establishment of heroin "shooting galleries". But there was no such suggestion in last year's Tory manifesto.

Ed Miliband swiftly distanced himself from his former cabinet colleague Bob Ainsworth's arguments last year in favour of drug legalisation, saying it would send out entirely "the wrong message".

But there is evidence that political leaders are lagging behind voters. Surveys suggest public opinion is shifting, with half of the public believing cannabis use should be decriminalised and 20 per cent taking the same view of all drugs.

Next month's move by Liberal Democrat activists is a significant moment: it will be the first time decriminalisation has been considered by a party in government. Equally significant is Nick Clegg's relaxed response. The odds are that a political party will fight the next election on a platform of widespread reform of drugs legislation.