Unease on the Tory right over David Cameron's coalition with the Liberal Democrats was highlighted last night in unguarded comments made by the man Cameron defeated in the 2005 Tory leadership campaign.

David Davis is reported to have approvingly repeated a description of the partnership between Cameron and Liberal Democrat leader Nick Clegg as "Brokeback Coalition", which he attributed to another senior Tory.

Davis made his remarks during a private lunch with former colleagues from Tate & Lyle at the Boot & Flogger wine bar in Southwark on Thursday.

The MP was reportedly overheard saying that Lord Ashcroft, the ex-Conservative party deputy chairman, had referred to the government as "Brokeback Coalition" – a reference to the Oscar-winning film Brokeback Mountain, about a gay relationship. Davis, whose remarks are disclosed in today's Financial Times, said he had been misheard.

Lord Ashcroft, the Tories' billionaire donor has been privately scathing about Cameron's general election campaign and says the Tory leader made a grave error in agreeing to take part in the television debates. He also shared the concerns of many frontbenchers that the main theme of the Tory election campaign – the "big society" – was too vague and was difficult to sell on the doorstep.

The FT went on to say that Davis, the former Europe minister, who recently led a successful rebellion against plans to make it more difficult for MPs to remove an unpopular government, was dismissive of Cameron's "big society". He reportedly called it "a Blairite dressing" for plans by the coalition plans to trim the state.

"The corollary of the big society is the smaller state. If you talk about the small state, people think you're Attila the Hun. If you talk about the big society, people think you're Mother Teresa."

Davis, who resigned from Cameron's shadow cabinet to lead a campaign against Labour plans for the detention of terror suspects without charge, told his audience he was enjoying his freedom on the backbenches. But he said there were not many jobs "unless you're female" because the Liberal Democrats had ushered few women into ministerial office.

Davis reportedly joked that David Laws, the former Lib Dem treasury chief secretary who resigned in May over his parliamentary expenses, was "one sort of minority" brought into government. Laws revealed at the time of his resignation that he is gay.

George Osborne, the chancellor, was given faint praise. Davis said that a newspaper headline that read "Osborne delivers" should have said "Osborne promises" on the grounds that he has not delivered anything yet.