Martin Bell, former sleaze-busting independent MP, said: “I am not against MPs employing members of their family, as long as they are up to the job.

“But there does need to be full transparency and I hope we are edging towards that. When I was an MP, I was effectively being asked to write blank cheques to myself every month.”

MPs can each spend up to £87,276 annually on employing researchers, secretaries and assistants and that total is soon to be increased to £96,630.

The latest edition of the Register of Interests of Members Secretaries and Research Assistants shows that nearly 40 MPs have wives or children working in their offices.

Some are unpaid. Westminster authorities say typical salaries range between £16,000 and £25,000 annually. In rare cases, secretaries can earn £40,000 a year.

Many more employ relatives in their constituency offices but are under no legal obligation to identify their staff.

Some critics suspect as many as one MP in six employs a family member.

Lib Dem MP Malcolm Bruce pays his wife Rosemary £28,500 a year to work in his office in his Gordon constituency, his office confirmed yesterday.

Sir Stuart Bell, Labour MP for Middlesbrough, employs his wife Margaret for £35,000 a year and Nick Ainger, Labour MP for Carmarthen West and South Pembrokeshire, pays his wife Sally about £19,000 a year. 

But most MPs do not release details of how much their staff are paid. It means the public cannot see how much MPs are paying their relatives.

A number of MPs contacted by the Daily Express yesterday confirmed that they were employing relatives in their offices.

Former Cabinet minster Peter Hain even lists his mother Adelaine Hain, 80, as an employee in his Westminster office.

Former Foreign Secretary Margaret Beckett names her husband Lionel as an employee.

Matthew Elliott, of the TaxPayers’ Alliance, said: “Taxpayers’ money must always be spent carefully and openly. The public are already concerned that some politicians are taking advantage of taxpayers financially, and this disgraceful example only deepens that concern. 

“It is in the interests of both the public and all MPs that the air is cleared. That can only be done by full disclosure of expenses and modern, transparent employment records. We have to make sure that this does not happen again. The public are understandably suspicious about MPs employing family members. 

“It is a practice that is basically confined to Westminster and would be pretty alien in any other workplace.” 

He added: “Politicians should be going out of their way to explain why they do it and to provide proof of work to reassure the public that taxpayers’ money is not being abused.”

Liberal Democrat MP Norman Baker, a campaigner against Westminster sleaze, welcomed plans from the National Audit Office for “specimen checks” on MPs’ staffing. But he opposed publishing publicly details of all staff names and salaries.

“There are ways of monitoring the system better without encroaching on people’s privacy,” he said.