The Lib Dem MPs referred their cases to the Commons watchdog
Four Lib Dem MPs have been told to apologise and repay money after breaching Commons rules over payments relating to second homes allowances.
They accepted one-off cash payments from the owners of an apartment block close to Parliament in return for agreeing to pay higher rent levels.
Richard Younger-Ross, John Barrett, Sandra Gidley and Paul Holmes will pay back about £16,500 in total before tax.
Lib Dem leader Nick Clegg praised the four for alerting the authorities.
No action has been recommended against two other Lib Dem MPs - Sir Alan Beith and Sir Menzies Campbell - who were also investigated.
Mr Barrett has been told to repay half the £11,234 he received less capital gains tax while Mr Younger-Ross must repay half of the £8,031 sum - after deducting tax - which he accepted.
Ms Gidley will have to repay a quarter of the £18,751 she received while Mr Holmes will repay a quarter of £9,440.
The inquiry was prompted by newspaper allegations last May that more than a dozen MPs had received thousands of pounds each in return for giving up the right to cheap rent on taxpayer-subsidised flats.
It was alleged the MPs were offered a cash sum by the new owners of the Dolphin House mansion block, used by MPs from all parties because of its closeness to Parliament, in exchange for moving out or paying more rent.
It was reported that many MPs accepted the money and remained in the flats, leaving the taxpayer to pick up the cost of the higher rental bills.
In his judgment on the case, Standards Commissioner John Lyon said all six Lib Dem MPs should have sought advice before accepting the money, the amount of which varied in individual cases.
He said none of the MPs had repaid the money when, because the sums were connected to publicly-funded claims for rent, they should have been surrendered to Parliament.
"Members who accepted the payments and did not pass them onto the House of Commons were in breach of the code of conduct because the decision of each member to accept and keep these financial offers had the effect of putting their personal interest above the public interest," the report said.
The report concluded that the four MPs were guilty of a "serious misjudgement" and the Commons Standards and Privileges Committee, which has the power to sanction MPs for misconduct, has ordered them to apologise and repay a fraction of the money.
Sir Alan Beith and Sir Menzies Campbell were found to have committed "lesser misjudgements" and face no sanctions.
Lib Dem leader Nick Clegg said the MPs concerned should be applauded for alerting the authorities to the case in the first place while other MPs living in the property had not.
"I am very pleased that Lib Dem MPs acted promptly and correctly in referring themselves and making clear they would comply with the recommendations of the committee," he said.
"In stark contrast, nearly a year later, Labour and Conservative MPs who accepted the offer from the Dolphin Square landlord have neither referred themselves nor been referred by their parties."
He said Labour and the Conservatives should now order "all their MPs who accepted these payments to immediately refer themselves to the Parliamentary Commissioner for Standards".
The Standards and Privileges Committee said it was aware other MPs had received "cash windfalls" but said it had no information about these cases as they had not been referred or the subject of complaints.