Coverage of the complicity of the Lib Dems in the coalition government in the abrupt trebling of university tuition fees after having been so robustly against any rise in the election campaign has dwelt largely on the political consequences for the coalition and the party - will it split the party, sink the coalition, lose Lib Dem seats in university towns and cities?  I live in Cambridge where the Lib Dem MP, Dr Julian Huppert, no doubt well aware that Anne Campbell, the then Labour MP, lost the seat in 2005 over the imposition of rather more moderate charges, is hawking his conscience around the local media, pledging to campaign against the rise. (Dr Huppert assured me at an election husting that PR was at the heart of his politics; I was surprised later to hear him on BBC radio extolling the virtue of the Alternative Vote.) There is a certain amount of derision, too, for Vince Cable's astonishing assertion that the rise is designed to enable more poorer students to go to university. 

But there is a very significant breach of constitutional convention, not to mention mere trust, in this remarkable somersault in the Liberal Democrat position.  Who didn't see the prominent campaign photographs of Nick Clegg with numerous Lib Dem candidates across the country, with the pledge to stand firm against a rise in student fees?  

Election pledges are integral to public understanding of the electoral process and amount to a genuinely popular constitutional convention. The public is given the opportunity at election time to weigh up the rival promises and policies of the parties standing for election and to choose between them. That's why the parties issue their manifestos. The process is underpinned to some degree by the first past the post electoral system which has generally made it possible for the party that 'wins' an election to carry out its policies. There has been some scepticism among ordinary people about whether they do or not, but by and large the parties respect this convention and do seek to implement their 'mandates'.

This is the first time in UK government that the Lib Dems have had to consider their attitude to this convention. Apparently, Norman Lamb MP has already re-defined the reach of the convention.  The pledge against any increase in university fees was 'a legitimate position for an opposition party to take',  but 'a very different position for a party with responsibility'. 

I don't want to be too po-faced about the Lib Dems' conduct, but surely, first, an opposition party is under a responsibility to advocate workable and 'responsible' policies at elections; and secondly, if they then enter into coalition government, to stick to the prominent pledges that they have advanced.