"His last-minute conversion to an inquiry into MPs' expenses has more to do with diverting attention from embarrassment about the expense claims of yet another of his ministers than any desire for real change.
"This is a case of too little too late from a prime minister who failed to ask the right questions about the activities of his own employment minister."
Mr McNulty has claimed £60,000 since 2002 for the house in his Harrow constituency - 11 miles from the House of Commons - where his parents live.
He moved into his main home in Hammersmith in 2002 when he got married but continued to claim expenses on his Harrow house.
Tory MP Greg Hands has lodged an official complaint about Mr McNulty's second home expenses claims.
He asked Parliament's standards commissioner John Lyon to look into whether rules were breached.
Mr McNulty himself said the regulations should be looked into.
Map showing distance from Tony McNulty's home to Westminster and his parents' home for which he claimed expenses
All MPs, apart from the 25 who represent inner London constituencies, can claim up to £24,000 a year in allowances towards the cost of staying away from home while on parliamentary business.
Mr McNulty said he made "considerable" use of the Harrow property and that it allowed him to do his job more effectively - but had stopped claiming the allowance in January because the fall in interest rates meant he could afford to pay the mortgage from his MP's salary.
His spokesman has said the MP is "completely compliant with all the regulations around the allowances for second homes".
A new system of expenses is due to come into force on 1 April.
Liberal Democrat leader Nick Clegg, said: "We should get rid of this charade all together and stop any MPs living in commuting distance from claiming this allowance at all."
Home Secretary Jacqui Smith has defended claiming about £116,000 for her family home in the West Midlands after declaring her sister's property in London - where she stayed four days a week - as her main residence.
She said the Commons authorities had approved her conduct. The parliamentary standards watchdog has asked her to justify her arrangements.
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