Four Liberal Democrat MPs were ordered today to apologise to the House of Commons and repay money after an inquiry into cash they received from the landlord of taxpayer-funded second homes in Westminster.
John Barrett, Sandra Gidley, Paul Holmes and Richard Younger-Ross showed "serious misjudgment", the House of Commons Standards and Privileges Committee said.
No action was recommended on lesser "misjudgments" by Sir Alan Beith and former party leader Sir Menzies Campbell.
Lib Dem leader Nick Clegg said the six - all tenants of Dolphin Square near Parliament, which houses many MPs' flats - had referred themselves to the Parliamentary Commissioner for Standards and urged Gordon Brown and David Cameron to order their MPs with second homes in the apartment block to do the same.
Mr Clegg said: "I am very pleased that Liberal Democrat MPs acted promptly and correctly in referring themselves to the Parliamentary Commissioner for Standards and making clear that they would comply with the recommendations of the committee.
"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.
"If they want to be taken at their word on clearing up the system of expenses and allowances, Gordon Brown and David Cameron must instruct all their MPs who accepted these payments to immediately refer themselves to the Parliamentary Commissioner for Standards and cooperate fully with him over this matter."
The six referred themselves to the committee after The Daily Telegraph reported that at least 13 MPs had received "windfalls" for giving up their rights to cheap rents in the block following its sale to a private company in 2005.
The paper said that a number of those who took the money then stayed on in the block - which was previously owned by a non-profit making trust - leaving the taxpayer to pick up the cost of the higher rentals.
In its report, the committee said that the public purse should not have lost out as a result of MPs accepting offers from Dolphin Square.
"We consider that Members should have sought official advice at the time the offers were made and we are surprised that none of the six who referred themselves did so," it said.
"If Members had sought advice in writing, they should have been advised to recognise the contribution made from public funds to the position they were in and to have paid a proportion of any windfall payment to the House.
"However, those who kept the payment and achieved a saving to public funds are, in our judgment, in a different position from those who kept it but did not achieve a saving, or who added to public expenditure."
Mr Barrett was ordered to pay half the £11,234 he received from the new owners of Dolphin Square, less any capital gains tax he paid.
Mr Younger-Ross was told to pay half the £8,031 which he received, less capital gains tax.
Ms Gidley was ordered to pay a quarter of the £18,751 she received, less capital gains tax.
And Mr Holmes was told to pay a quarter of the £9,440 which he received, less capital gains tax.
The Parliamentary Commissioner for Standards, John Lyon, who carried out the investigation for the committee, said its ruling could have "significant implications" for other MPs who had flats in Dolphin Square, which has long been popular with parliamentarians.
"The key point, I believe, is that it was the payments from parliamentary resources, sometimes over many years, which put each member in the position of being offered a sum of money, in effect, to buy out their rights as protected tenants," he said.
"In my judgment, public funds should have benefited from the acceptance of any offer arising from these rental payments. And, in my judgment, public funds should have benefited to the full.
"The effect of members not making over these payments to the House was to put their private interest above their public interest, contrary to the Code of Conduct for Members of Parliament."
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