Treasury Minister David Laws 'should step aside'
David Laws has faced a call to "stand aside" from his post as Chief Treasury Secretary after he admitted claiming expenses to pay rent to his partner.
Former Commissioner for Standards in Public Life Sir Alistair Graham said Mr Laws should remove himself while an investigation is carried out.
Mr Laws has apologised and said he will pay back the money which the Daily Telegraph said totalled £40,000.
The Lib Dem MP said he wanted to keep his relationship with the man private.
In a statement Mr Laws said he "deeply" regretted the situation. He told a newspaper the revelations had given him "the most difficult day of [his] life".
The Yeovil MP has referred himself to the Parliamentary Standards Commissioner - a decision supported by Prime Minister David Cameron.
One Labour backbencher called on Mr Laws to resign, but his fellow Liberal Democrats - including former party leader Lord Ashdown - gave him their backing.
Lord Ashdown described the story as a "personal tragedy".
Mr Laws fell foul of parliamentary rules introduced in 2006 banning MPs from "leasing accommodation from a partner".
According to the Daily Telegraph, he claimed up to £950 a month for eight years to rent a room in two properties owned by his partner, James Lundie.
Mr Laws said he claimed back the costs of sharing a home in Kennington, south London, with Mr Lundie from 2001 to June 2007.
He said his partner bought a new home, in London, in June 2007 and he continued to claim back his share of the costs until August 2009.
The minister said he extended the mortgage on his Somerset property to help Mr Lundie purchase the new property.
Sir Alistair said it was a shame to see expenses back in the news.
"I think all of us hoped that after the General Election, a line could be drawn - we've got a new independent Parliamentary standards authority - that we would be in a new era of transparency and cleanliness as far as our politics are concerned. Now there's a bit of a question mark."
He added the revelations made Mr Laws's position very difficult.
"At a minimum he should step aside while the Parliamentary Commissioner for Standards carries out his investigation and reports to the Committee on Standards and Privileges."
Mr Laws said: "At no point did I consider myself to be in breach of the rules which in 2009 defined partner as 'one of a couple… who although not married to each other or civil partners are living together and treat each other as spouses'.
"Although we were living together we did not treat each other as spouses - for example we do not share bank accounts and indeed have separate social lives.
"However, I now accept that this was open to interpretation and will immediately pay back the costs of the rent and other housing costs I claimed from the time the rules changed until August 2009."
He added: "My motivation throughout has not been to maximise profit but to simply protect our privacy and my wish not to reveal my sexuality.
"I regret this situation deeply, accept that I should not have claimed my expenses in this way and apologise fully."
In an interview with the Times newspaper, Mr Laws said it had been the most difficult day of his life.
He said: "I apologise to James [Lundie], and to all my family, friends and constituents who I have not been honest with about who I am over all the years of my life."
A spokesman for Prime Minister David Cameron said: "The prime minister has been made aware of this situation and he agrees with David Laws's decision to self-refer to the Parliamentary Standards Commissioner."
Labour backbencher John Mann urged Mr Laws to resign, saying his position was "untenable".
"Nick Clegg was meant to have carried out an audit of his MPs in the last parliament. These things should have been out in the open," he said.
Fellow Labour MP Alan Whitehead, a member of the standards and privileges committee in the old parliament, said Mr Laws's position would become "very difficult" if it was decided that serious breaches of the rules had been made.
And Labour MP for Newport West, Paul Flynn, said the evidence against Mr Laws was "damning".
He wrote on his blog that Mr Laws would be judged more harshly because the Lib Dems had been "the most accusatory and self-righteous of all parties in the expenses scandal".
But former Lib Dem leader, Lord Ashdown, said the revelations were a "personal tragedy" for Mr Laws, describing him as "Mr Integrity".
Mr Laws's parliamentary colleague, the Liberal Democrat MP for Taunton Deane Jeremy Browne, said the matter was "a human story, not a financial story" about a "deeply private man".
"This is not about David being motivated by money," he said.
Mr Laws was one of five Liberal Democrats named in Mr Cameron's coalition cabinet following the election, working with Chancellor George Osborne at the Treasury.
A press release on Mr Laws's website, dated 18 June last year, said he had not "gained" through the taxpayer from buying a property because he rented accommodation in London.