Conservative leader David Cameron has been criticised by a standards watchdog for using his taxpayer-funded Commons office to raise money for the party.
Mr Cameron promoted lunches in his Commons office
The Commons Committee on Standards and Privileges called it "ill-advised" to offer meetings there in return for membership of a fundraising club.
It upheld a complaint by Lib Dem MP Norman Baker, who said such actions could undermine trust in all MPs.
Mr Cameron accepted the decision and apologised "unreservedly".
The complaint came after the Leader's Club, a Conservative fund-raising club, advertised benefits to members including the opportunity to meet Mr Cameron in his Commons office after prime minister's questions.
Since his election as Tory leader in December 2005, he has held seven such lunches.
The committee said: "Mr Cameron was in our view ill-advised to link directly, in promoting the Leader's Group, the issues of access to his office and party fund-raising.
"We agree with the commissioner that Mr Baker's complaint should be upheld.
"We are grateful to Mr Cameron for his speedy and full acceptance of the commissioner's recommendation, and for his apology to the House.
"We consider that this, and the undertakings he has given in his written evidence to us that he will ensure there is no repetition, adequately dispose of this matter."
The committee's findings followed a report by the Parliamentary Commissioner for Standards, Sir Philip Mawer, who said Commons facilities were not intended to boost party finances.
In his report to the committee, he said the fundraising purpose of the Leader's Group was clear, as was the fact that members had been offered access to Mr Cameron's office.
He went on: "While there is no reason in principle... why Mr Cameron cannot meet, in his office or elsewhere in the Parliamentary estate, those who donate to his party, what neither he nor his party... can properly do is employ their parliamentary office as part of a party fundraising stratagem.
"In my view, that is, on the facts, precisely what happened in this case."
Mr Cameron said his contravention of the MPs' Code of Conduct had been "inadvertent".
He added: "I would like to assure the committee that this will not happen again.
"I will not hold lunches for members of the Leader's Group in my parliamentary office in the future, nor will my office be mentioned in any promotional literature."
A Conservative Party spokesman said: "We always made clear that we wanted to see the rules relating to the use of banqueting facilities clarified and we welcome the fact that the Committee on Standards and Privileges has now made a recommendation on this."
The committee also said fundraising political clubs should not use parliamentary facilities in future, following separate complaints.
Labour MPs John Mann and Kevan Jones claimed 26 Tory MPs had used Commons dining rooms to entertain members of party fundraising clubs.
Those accused included shadow chancellor George Osborne and former leader Michael Howard.
The committee said it would "not be right" to single out particular MPs for criticism.
"However, we are strongly of the view that practice generally in respect of the use of private dining facilities of the House by organisations raising funds for political parties has given the impression that House facilities have been used improperly for party fund-raising, and is in need of reform," it added.
Sir Philip suggested fundraising clubs should be allowed to use Commons facilities as long as the events are charged for separately and are not promised in promotional material.
But he criticised Mr Mann and Mr Jones for informing the media of their complaints before some of the MPs concerned.
Mr Baker said: "Whilst Mr Cameron's actions will unfortunately raise further doubt in the public mind about the conduct of MPs in general, I hope that the public will nevertheless both appreciate that a system for complaining about such misconduct is in place and that they can have confidence that the mechanisms in place for dealing with improper behaviour do work."