Liberal Democrat MP David Laws has apologised for his expenses claims after he was found to have wrongly claimed £40,000 in rent paid to his boyfriend.

The former chief secretary to the Treasury resigned from the Cabinet last May after the claims were revealed. He claimed that he wanted to keep his sexual orientation secret.

After an investigation, a Commons committee and the Parliamentary Commissioner for Standards, John Lyon, concluded today that he committed “a series of serious breaches of rules” for money he claimed from the taxpayer.

Yeovil MP Mr Laws is to be suspended from the Commons for seven days – a rare punishment seen as second in severity to expulsion. The suspension will begin on June 7th. He will also apologise to parliament.

The commissioner found that Mr Laws should not have been paying rent to a partner but said: “Mr Laws’ desire for secrecy led him to act in a way which was not compatible with the standards expected of an MP”.

It was also found that he had claimed for maintenance and repair costs for the London property. While these may have been acceptable if he was a cohabitant, Mr Laws was a lodger.

Mr Laws had lived with his boyfriend, the lobbyist James Lundie, for seven years. In 2006, Commons rules changed to bar MPs claiming expenses for rent paid to partners or family members. Mr Laws says he did not declare the relationship because he wanted it to stay a secret.

Mr Lyon wrote: “I have no reason to doubt that Mr Laws’ primary motivation was to keep secret the sexuality that he had kept hidden. . . I have no evidence that Mr Laws made his claims with the intention of benefiting himself or his partner in conscious breach of the rules.”

The committee and commissioner found that the MP had already repaid £56,592 – the full amount of his second home allowance claims between July 2006 and July 2009.

They accepted that the MP could have claimed “considerably more” under Commons rules if he had been open about the relationship.

In a statement, Mr Laws said: “I accept the conclusions of the inquiry and take full responsibility for the mistakes which I have made.

“I apologise to my constituents and to Parliament. Each of us should be our own sternest critic, and I recognise that my attempts to keep my personal life private were in conflict with my duty as an MP to ensure that my claims were in every sense above reproach.

“I should have resolved this dilemma in the public interest and not in the interests of my privacy.

“However, from the moment these matters became public, I have made clear that my motivation was to protect my privacy, rather than to benefit from the system of parliamentary expenses, and I am pleased that the Commissioner has upheld that view.

“I have also, from the very beginning, made clear that I believed that my secrecy about my private life led me to make lower overall claims than would otherwise be the case, and this has been confirmed by the Parliamentary Commissioner and by the committee.

“The taxpayer gained, rather than lost out, from my desire for secrecy, though I fully accept that this is not an adequate reason for breaking the rules.

“This last year has been a difficult one, and I am grateful to family, friends, constituents and colleagues for their support and understanding.”