MPs will have to pay back any overpayments of allowances they have received in the past five years, Harriet Harman said today.

Since the expenses row exploded in the early summer, Sir Thomas Legg has been leading a review of every claim made by every MP. He is expected to report in November.

He will soon be writing to all MPs individually, giving them a chance to comment on his findings and ensure that they are factually correct.

But Ms Harman said that the repayment of any claims which were not within the rules was a necessary part of reforms to clean up Parliament that should be in place before the next general election.

That would mean that the electorate would be voting for a more transparent and better regulated House, in which those who had broken expenses rules had been been punished, the Commons Leader said. She added: “Any overpayments will be paid back.”

The Parliamentary Standards Act gives the new Independent Parliamentary Standards Authority (IPSA) power to deduct past overpayments from MPs’ future claims, and Ms Harman emphasised that this power would be used.

Her remarks could have serious implications for many MPs. In the Legg review all MPs — not only those who featured in the disclosures about expenses claims over the summer — have been examined, and many have saying privately that they will face hardship if forced to pay everything back.

In a speech to the Centre for Public Policy Seminars think-tank in London, Ms Harman said this was “a critical time for parliamentary democracy in this country”.

She added: “Our Parliament has suffered much self-inflicted injury, and we all recognise that it is imperative that we make every effort to rebuild trust in modern democratic Britain — not just for the sake of our politicians but for the sake of our citizens who need and are entitled to an effective democracy in which they can trust.”

The Committee on Standards in Public Life is due to report this autumn with recommendations for a fairer and more robust allowances system.

Those rules will be overseen by the IPSA, which will start work later this year.

Ms Harman said: “It is not enough for the claims in the future to be clear, transparent and robustly audited.

“We have to deal with the past in a way that commands public confidence. It is not enough for past over-claims to be identified and exposed to public scrutiny. They need to be paid back.

“When social security benefits are overpaid, even where it is simply a mistake, they have to be paid back. The same principle must apply to MPs.

“If they were not fully within the rules as they obtained at the time, allowance payments must be paid back.”

She pointed out that reforms were also being considered to strengthen the role of backbenchers in holding the Government to account.

She stressed that more women were needed in the chamber to increase diversity.

“Though the House of Commons is much more representative of our diverse ethnic communities, and though women are better represented now than they were when I first entered Parliament in 1982, there is still a long way to go,” she said.

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