A few months after the coalition was formed, I asked a young Liberal Democrat adviser, newly catapulted from the sleepy suburbs of opposition to the bustling centre of power, whether his family was impressed by the move. “My mum is proud,” came the response, “but she did say, ‘Does it have to be with the Tories, love?’”

It did. The distribution of seats in parliament would not have permitted any other combination to form a workable government. But the plaintive tone of the question summarises Lib Dem discomfort. The price of entry into the Westminster big league was conjugation with a party to which liberal Britain has been historically allergic. Nick Clegg knew that there were problems with the Tory brand but he underestimated how stubborn and contagious they would be. It is hard to mobilise a party to defend its record when it is constantly fighting the urge to apologise instead.

The demoralisation is mutual. A Conservative MP recently described for me his dilemma over the party’s policy on gay marriage. After some  soul-searching, he had accepted the logic of David Cameron’s support for the idea but his family remains appalled. He skipped church one Sunday when the issue was making headlines.

The Conservatives’ fear of ostracism on Shire pews and the snubbing of Lib Dems at metropolitan dinner parties are expressions of the same problem for the coalition. Clegg and Cameron have invested all of their political capital in the venture but their MPs and members feel none of the emotional attachment required to carry a government through rough patches. Many are ashamed of policies that they are supposed to promote. In such conditions, loyalty rots.

The usual suspects

The Tories are more openly rebellious, not because their sacrifice is greater but because their expectations before the election were higher. With ex-ministers and veterans of Margaret Thatcher’s hegemony on the Conservative side, there was more surface area of ego to be bruised. A battering in local elections on 3 May has revived backbench demands for a more assertive Tory agenda. Cameron is under pressure to prove his carnivorous credentials by chewing up emblems of liberal compromise: House of Lords reform; wind-farm subsidies; gay marriage. They should be replaced with toughness on the things Tories are always tough on: Europe, immigration, crime, human rights and labour protection laws.

Downing Street is determined not to capitulate to those demands, or rather not to be seen to cave in. Cameron’s position is not so strong that he can afford to provoke the notoriously regicidal temper of his back ranks. At the same time, private opinion polls tell him it was the failure to neutralise the Tories’ reputation for flint-hearted fanaticism that cost him a majority at the last election.

One No 10 source describes the proposal to solve Conservatives’ problems with a sharp turn to the right as “demonstrably absurd”. Special contempt is reserved in Team Cameron for the suggestion that duff election results can be explained by an excess of social liberalism. “The idea that we lost seats because of gay marriage or anything like that is just false,” says an aide. The demands for a change of course are dismissed as carping by “the usual suspects” – losers in old leadership races and career troublemakers.

There is dangerous complacency in that attitude. Tories from all corners of the party voice dismay about the way coalition has been handled. “There is a feeling of being consistently out-negotiated by the Lib Dems,” says one usually Cameron-friendly MP. Reports from the electoral front line confirm that the gay marriage issue caused untold harm by inciting party stalwarts to stay at home. Mass abstention by supporters of the coalition parties, ceding the field to more motivated anti-incumbent forces, was the biggest factor in Labour’s acquisition of more than 820 council seats. Two-thirds of the electorate didn’t express a preference at all. The most dynamic force in British politics is the despondent tide pulling voters away from the three main Westminster parties.

That trend poses a unique hazard for Clegg. Bridges back to the kind of party the Lib Dems used to be before coalition are burned. There can be no more mopping up of protest votes and harbouring Labour refugees from Blairism. But forging a new identity while shackled to the Tories is proving fiendishly difficult. The biggest strategic issue – the austerity programme – is settled and non-negotiable. That leaves the junior partner fishing for definition around the policy margins. Even where credit is due for big and popular measures (raising the tax threshold for low earners; the pupil premium), it is lost in accusations of complicity in the bigger, unpopular ones (NHS reform; public-sector cuts). The process of barter and compromise that allows the Lib Dems to implement chunks of their manifesto seems to reinforce the impression that coalition is about selling principle for power.

Vanity rides

Clegg’s allies know that is the deadliest charge against them. I have heard one Lib Dem minister sound envious of the way his Conservative colleagues are hated for their ideology. It proves at least that people know they have an ideology. There is a special indignity in being reviled for seeking vanity rides in government cars.

There was a moment in the spring of 2010 when coalition government looked like an innovation capable of addressing disaffection with politics. The image of rivals coming together to tackle a national economic emergency was popular. But the emergency is untackled. The economy is shrinking; the national debt is rising. The eurozone threatens to dissolve in chaos. The two governing parties’ instinctive responses to those problems are usually divergent, often incompatible. As Cameron tries to balance the competing demands of his party’s right wing and his Lib Dem partners, the whole enterprise looks like a cynical commerce in second-tier issues – a game that keeps MPs, journalists and civil servants busy without adequately addressing the country’s problems. That is Clegg’s most harrowing nightmare: coalition as the distilled essence of Westminster poison instead of the antidote.