Ms Harman said voters wanted to know taxpayers' money was being spent properly, adding that the case of disgraced MP Derek Conway had cast an "unwarranted shadow" over Parliament.

She said she was "horrified" by the conduct of the Old Bexley and Sidcup MP, who still faces the threat of a criminal investigation into his use of public funds to pay his full-time student son as a researcher.

He was suspended from the Commons for 10 days and thrown out of the Tory party for overpaying his son for "all but invisible" research work at the expense of taxpayers - and will step down as an MP at the next general election.

And Ms Harman, who is leader of the House of Commons, defended its Speaker Michael Martin, who has come under fire over the use of Commons allowances by himself and his wife Mary.

She was speaking following proposals last week from the Standards and Privileges Committee to force MPs to publicly declare the names and jobs of family members they employ at taxpayers' expense.

It said the rules should come into force in April but could be made voluntary until July to give time to deal with any technical or legal issues involved.

Ms Harman told a television interview: "It is very important that MPs can properly hold the Government to account and to do that they need a proper office once they are elected.

"But the public need to absolutely sure there is a proper system for validating claims and there is not abuse. We were all horrified by the case of Derek Conway. Not only was it absolutely wrong but it cast a shadow over all MPs. All MPs are really dismayed by that."

Asked if MPs allowances should be made available to their constituents she said: "There are some issues around the personal privacy of family members of MPs which will have to be sorted through. If it is public money, by and large the public want to know how public money is being spent and they want to know it is spent properly."