Political revenge is another dish best served cold, as the Liberal Democrats are discovering. Cannibalised by their Coalition “partners” at last year’s general election, the Lib Dems are now shining a very unflattering light on the Conservatives and undermining David Cameron’s attempt to portray them as a “modern, compassionate, One Nation government”. They have also put another cloud over George Osborne as his hopes of succeeding Mr Cameron dwindle.

Tory ministers dismiss the flurry of Lib Dem attacks as sour grapes from a defeated and dejected party that saw its number of MPs cut from 57 to just eight and is now off the radar. But this is unfair. The Lib Dem accounts of the five-year Coalition Government are given by people who know where the “nasty party’s” bodies are buried – because they were there.

When I interviewed Nick Clegg last month, he was most definitely not bitter. I invited him repeatedly to complain about how the Tories ruthlessly seized Lib Dem seats by warning that they would hop into bed with Labour and the SNP in a hung parliament. Mr Clegg refused the bait, saying there is no point in “whingeing” when you lose.

But the former Deputy Prime Minister gave me a revealing insight as he argued that Mr Cameron, without the need to secure Lib Dem support, is squandering the Coalition’s “progressive legacy.” Mr Clegg recalled that when the Lib Dems repeatedly proposed more public housebuilding to relieve the housing crisis, they were rebuffed by this crude Cameron-Osborne response: “All it does is to produce more Labour voters.”

Further evidence of the Tories’ narrow, partisan approach emerged this week in a riveting book, Coalition, by David Laws, the former Schools Minister (published by Biteback). He details how Mr Clegg acted as a brake on Mr Osborne’s constant demands for welfare cuts. He writes: “The Lib Dem leader thought that a major weakness of both David Cameron and George Osborne was that they had little sympathy with or understanding of people on very low incomes, and were inclined to write them off politically as ‘not our voters’.” Mr Clegg even considered ending his cherished Coalition over the Tories’ plans to “balance the books on the backs of the poor” while they “resolutely protected the rich”. Mr Laws says: “George Osborne saw ‘welfare’ as a big political dividing line. He wanted Labour to be seen as the party of ‘welfare scroungers’, and he hoped that the Conservatives could position themselves as the party of the ‘strivers’.” To help protect working-age benefits, the Lib Dems proposed cutting the winter fuel allowance and free TV licences for pensioners. Mr Osborne was prepared to bite the bullet; Mr Cameron wavered, but in the end judged that saving only £100m was “not worth the political hassle”.

If all this was coming only from the Lib Dems, we might dismiss it as a backward look at the Coalition through their end of the telescope. But the Lib Dem accounts are all the more convincing because Iain Duncan Smith made remarkably similar criticisms after his spectacular resignation as Work and Pensions Secretary last weekend. He echoed the claims that Cameron-Osborne saw the welfare budget as a cash cow; were balancing the books on the backs of the poor and got the old-young balance wrong by over-protecting pensioners. The result, he claimed, was that we were not “all in this together” after all. Most damagingly, Mr Duncan Smith argued that the Tories lost the mantle of “a One Nation party caring about those who don’t even necessarily vote for it, who may never vote for it”. Surely, a centre-left party and a right-wing Tory can’t both be wrong? This is toxic for a party desperate to detoxify itself and colonise the political centre ground.

There is more trouble ahead on this front. There are more Lib Dem books to come, including one from Mr Clegg himself in September – surely, another dish of cold revenge.

Some Tory ministers admit privately that they miss their former Coalition partners. Why? Because the need to square the Lib Dems meant there was a form of Cabinet government. Since the election, they say, most key decisions are handed down by Downing Street and the Treasury, and that no one else matters.

Mr Clegg’s constant claims that the Lib Dems “anchored the Coalition in the centre ground” cut little ice with the voters in May last year – many of whom, as Mr Laws concludes, never forgave their original decision to join forces with the Tories in 2010. But Mr Clegg was right, and the restraining hand of his party helped to blunt the Tory axe. In turn, this helped Mr Cameron win enough trust to secure an overall majority last year – a bitter irony for the Lib Dems, who did the right thing for the country in 2010, if not for themselves.

Most Tories did not expect to win the election. They thought their best hope was another Con-Lib coalition. Mr Osborne was almost certainly banking on the Lib Dems wielding a veto on some of the £12bn of welfare cuts in the Tory manifesto.