Four Liberal Democrat MPs have been ordered 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."
