Cabinet ministers face questions after full details of their expenses claims were published by the Daily Telegraph.
They include a claim for £6,500 made by Gordon Brown to pay his brother for a cleaner for his Westminster flat.
Minister Hazel Blears claimed for three homes in one year and spent nearly £5,000 on furniture in three months.
Mr Brown said the system did not work and had to change: "MPs have to live in two places. But we need a system that is better than the one we've got. "
Meanwhile Downing Street has released a copy of the contract for cleaning Gordon Brown's flat and said there was nothing "unusual or wrong" about the PM sharing a cleaner with his brother and reimbursing him for a share of the cost.
The Telegraph reported that Andrew Brown received £6,577 between 2004 and 2006 for cleaning services at the prime minister's private flat.
Defending the prime minister, deputy Labour leader Ms Harriet Harman told BBC Radio 4's Today programme: "It's being portrayed as if Gordon Brown somehow has pocketed extra money for it purporting to be his cleaner, or his brother has pocketed extra money, and that's not the case."
She said all claims were within the rules.
"I know this looks bad and people are angry," she said.
"MPs believe in the cause of public service and that's why they're in public service and I believe our House of Commons is not scarred by corruption on the scale of other political systems."
"We have recognised that the allowances system needs to change, but people have claimed in good faith under the old system - we've already changed the old system and we're going to change it further."
Asked about claims MPs have been claiming one property is their "second home" under the allowance, but not for the purposes of council tax or capital gains tax, she refused to give a "gut instinct judgement" on whether it was a breach of the rules.
But she said: "Normally it would be the same for council tax, for tax if there was a sale of the property... normally there would be a consistency on that."
Full details of all MPs' expenses dating back four years, running to 2.4 million receipts, were due to be published in the middle of July after the Commons authorities lost a Freedom of Information battle.
But the Telegraph claims potential abuses would have remained secret because MPs have been allowed to edit out addresses and other information.
The newspaper has published details of 13 cabinet ministers, including chancellor Alistair Darling, Communities Secretary Hazel Blears and Culture Secretary Andy Burnham.
It plans to publish further revelations about MPs from other parties as well as Labour over the next few days.
The Telegraph reported that Gordon Brown also claimed £153 twice for the same plumbing work at his constituency home - which No 10 said was done inadvertently and had been repaid.
Justice Secretary Jack Straw claimed his entire council tax bill for his second home despite already enjoying a substantial discount from his local authority, worth a reported £1,500 a year.
His spokesman said all his claims were made within Commons rules and he had repaid it when he spotted the mistake.
Among other revelations, Ms Blears is said to have claimed for expenditure under the allowance on three different properties during the same year, spending £5,000 on furniture in three months.
The Telegraph says by switching their designated second home between their London and constituency properties, Ms Blears and other MPs have been able to claim for household goods or other reimbursements for both.
Jack Straw is under scrutiny for his council tax claims
A spokesman for Ms Blears said she had done nothing wrong and the furnishings she had bought were "reasonable".
"Hazel is honest as the day is long," said the spokesman.
Business Secretary Lord Mandelson claimed for improvements on his constituency home after he announced he was leaving Parliament to become an EU Commissioner. He later sold the property for a profit of £136,000.
He rejected claims he used taxpayers' cash to "renovate" his home for profit, insisting the money was spent on essential maintenance.
He said the Telegraph's report - which details a £1,500 gardening bill and £1,350 in house repairs - was presented to provoke public anger.
"The fact is that these allowances would not have been paid if they weren't within the rules," he told BBC Radio Scotland's Good Morning Scotland programme.
We do respect public opinion and we do respect the need for change
Culture Secretary Andy Burnham was in correspondence with the fees office for eight months over an expenses claim for £16,500 to buy and renovate a new London flat.
Officials finally agreed to pay the cash after rejecting the claim three times.
This followed a series of letters from Mr Burnham asking for his expenses to be paid urgently.
Mr Burnham says that over the past five years he has under-claimed on the Additional Costs Allowance by about £40,000.
The Telegraph accuses MPs of trying to maximise the amount of money they can legitimately claim within the rules, which they set and oversee.
Labour MP Sir Stuart Bell, who sits on the House of Commons Commission, said the expenses claims were "not unusual" or "out of order".
He added: "We do respect public opinion and we do respect the need for change - and I think that change is coming, I hope it will come quicker and I hope the public will get the respect for MPs back which we do actually deserve at the end of the day."
The Telegraph has not confirmed whether it paid for the information.
No 10 sources suggested the information published was accurate but insisted the nature and timing of the publication was politically motivated.
MPs recently voted through reforms of the expenses system amid mounting public anger about alleged abuses and will now have to provide receipts for all spending.
But they have still to reach a cross-party agreement on reforming the controversial second homes allowance. The Committee on Standards in Public Life is also conducting a review of pay and expenses after concerns public trust had fallen to an all-time low.
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