Former deputy prime minister Nick Clegg has accused George Osborne of "cynically" cutting welfare without caring about the impact on the poor when he was chancellor because it boosted Tory support.
Mr Clegg said Downing Street was also suspicious of investing in social housing during the coalition government because it feared it would "create Labour voters."
Branding the attitude of Mr Osborne "very unattractive, very cynical", Mr Clegg told The Guardian: "Welfare for Osborne was just a bottomless pit of savings, and it didn't really matter what the human consequences were, because focus groups had shown that the voters they wanted to appeal to were very anti-welfare, and therefore there was almost no limit to those anti-welfare prejudices."
Slamming the approach of David Cameron and Mr Osborne to spending on social housing, Mr Clegg said he was rebuked by one of the two when he raised the issue.
"I honestly can't remember whom, looked genuinely nonplussed, said: 'I don't understand why you keep going on about the need for more social housing - it just creates Labour voters'. They genuinely saw housing as a petri dish for voters. It was unbelievable."
The ex-Lib Dem leader accused Theresa May of trying to have misleading numbers inserted into a Home Office study of immigration when she was in charge of the department.
"She kept saying there was this terrible 'abuse' of freedom of movement, when simply describing EU citizens exercising their right to come and work in the UK. They tried to insert statistics suggesting the number of UK citizens living and working in other EU countries was half a million lower than any other mainstream estimate," he said.
Accusing the now Prime Minister of pandering to the "cardboard cut-out prejudices in the Tory party", Mr Clegg said: "That's clearly what she and her team were doing when they were trying to insert erroneous facts into this report on freedom of movement."
Mr Clegg said he now realised breaking the Lib Dem pledge not to increase tuition fees had been a major mistake, and he considered quitting government when his popularity slumped as a result.
The Lib Dem MP said the decision to back tripling tuition fees to £9,000 was something the party never recovered from.
"Getting your kids into university, seeing them in a gown on the mantelpiece, it's the distillation of a better life for your children. I have spent a lot of time thinking about the emotional pungency of it. It's like a politician coming out of the television going 'Bang!' to my face as a parent. That's my explanation," he said.
Mr Clegg said his wife and children had teased him when his apology for the tuition fees decision went viral as an internet song called I'm Sorry.
The Lib Dem MP said other big mistakes included the overly friendly Downing St garden press conference at the beginning of the coalition, and sitting next to Mr Cameron during prime minister's question time.
Mr Clegg said that ex-Lib Dem leader Paddy Ashdown berated him for being overweight after he stopped exercising due to the pressures of the job and as a result and looked "fat, pale and unhealthy".
The ex-deputy PM said the claim the Queen had vented her fury at the EU during an official dinner was "complete rubbish", which he said had been leaked by leading Brexit campaigner Michael Gove.
Mr Clegg also defended his wife Miriam Gonzalez Durantez after eyebrows were raised when she criticised Samantha Cameron for serving the couple roast chicken with Hellman's mayonnaise on the side, saying: "To be fair to Miriam, unless you're very sensitive about your own mayonnaise, I don't think that counts as score-settling."
Scottish First Minister and SNP leader Nicola Sturgeon hit out at Mr Clegg's admissions saying: "How many vulnerable people could have been spared misery if the Lib Dems had spoken out about this at the time?"