The first official list, published in the wake of the scandal which cost the former Tory MP Derek Conway his political career, showed that MPs of all parties have close relatives on the public payroll.

It includes senior figures such as the Home Secretary, Jacqui Smith, the Environment Secretary, Hilary Benn, the Housing minister, Caroline Flint, the shadow Home Secretary, David Davis, and the former Tory leader Michael Howard.

Five MPs employ more than one member of their family. The new Democratic Unionist Party leader, Peter Robinson, and his wife Iris, who is also an MP, employ all three of their children as well as a daughter-in-law.

Others included on thelist are the Tory MP Sir George Young, chairman of the Commons Standards and Privileges Committee, and Sir Stuart Bell, the Labour MP who is among the senior politicians reviewing Commons expenses.

The current register is voluntary, and there are indications that many MPs have yet to declare their family employees. In February, David Cameron said more than 70 Conservative MPs employed family members, but yesterday's list showed only 39 Conservatives registering their relatives' employment.

It has been voluntary for MPs to name the family members that they employ since 1 April, although party leaders have urged them to do so. Registration will be compulsory from August.

The register was released late yesterday afternoon when many MPs had left Westminster for the week. Its publication was agreed earlier this year after Mr Conway was suspended from the Commons and stripped of the Conservative whip for misusing public money to pay his son tens of thousands of pounds as a researcher while he was a full-time student in Newcastle.

Ms Smith is the most senior cabinet minister on the list. She employs her husband, Richard Timney, as a senior research/parliamentary assistant. He will be earning between £27,780 and £40,052. Her cabinet colleague Hilary Benn employs his wife, Sally Clark, as a research/parliamentary assistant. The pay range for such a post is between £14,212 and £34,240.

Ms Flint, who attends the Cabinet, employs her husband, Phil Cole, as her office manager on a salary of between £21,320 and £40,052. Mr Howard discloses that his wife, Sandra, acts as a part-time secretary, while Mr Davis employs his wife, Doreen, as executive secretary.

Liberal Democrats on the register include Malcolm Bruce, Paul Burstow and David Heath, who all employ their wives.

There is no suggestion that employing family members breaks any parliamentary rules. Many MPs insist that close family members are well suited to the awkward hours and highly personal nature of political work. MPs say their relatives often work far longer hours than other employees would be prepared to accept.

Some backbenchers privately argue that their marriages have been strengthened by working alongside their spouses in the highly stressful environment of the Westminster village.

But Matthew Elliott, chief executive of the TaxPayers' Alliance, said: "This is a completely outdated practice that raises people's suspicions about politicians' motives. To ordinary taxpayers, Parliament is an excessively generous gravy train at the best of times, but the fact that so many MPs employ family members is simply unacceptable. To dispel any suspicion that they are taking advantage of taxpayers' generosity, this practice should be banned once and for all."