There have long been suspicions that some MPs may be using parliamentary allowances to bolster their family incomes.

Up to £87,276 annually - soon to be increased to £96,630 - is on offer to each MP to fund researchers, secretaries and assistants to staff their offices, and it is up to them who they employ.

The cash is intended to provide for about three members of staff, and dozens of MPs are thought to recruit spouses, children or other relatives to fill some of these posts.

MPs are perfectly entitled to employ members of their own families. In many cases, their wife - or occasionally husband - is a vital member of staff, putting in long hours’ labour on political research or constituency casework.

But nonetheless, suspicions abound that some spouses or children may be recruited less for their secretarial skills than as a means of keeping the money in the family.

Proving it is a different matter. So long as the relative attends the MP’s Westminster office reasonably regularly, it is difficult for anybody to know exactly how much work he or she is doing.

Derek Conway’s difficulties arose because his son Freddie - according to the Commons Standards and Privileges Committee - was “all but invisible” at Westminster, having “little or no contact” with his father’s office while a full-time student at Newcastle and leaving “no record” of having done any work. Despite this he was paid nearly £45,000 in salary and bonuses over three years, plus pension contributions worth a further £4,500.

Iain Duncan Smith, the former Tory leader who was cleared in 2004 of wrongdoing over his employment of wife Betsy as a diary secretary, told BBC2’s The Daily Politics: “There is nothing wrong about people employing... their wives, or whatever, providing they do the work and providing it fits with the contract.

“The key question is did it for Derek Conway, and the committee found that it did not...

“Whether it is a Labour or Conservative MP who has been caught on this and is found wanting, the truth is that it brings the whole process into disrepute and I think that is the biggest problem for all of us.”

Funding for staff forms only part of a system of allowances and expenses, however, which last year saw MPs rack up a total bill of £87 million - an average of £137,000 each.

Despite bitter protestations from MPs to the contrary, there are widespread claims that many of the allowances available amount to a top-up to their salaries of £61,820.

Members of the Commons are entitled to claim up to £22,100 a year to maintain a second home if their constituency is outside central London - even in easily commutable locations in the outer suburbs of the capital.

There is no limit on travel costs for “Parliamentary business”, and MPs are free to choose their mode of transport. Driving brings in 40p per mile, while they receive 20p per mile for cycling.

Last March, the Commons also voted itself another £10,000 each in “communications allowance” which should be used to promote “public understanding” of Parliament.

Unlike most workers, a great deal of faith is put in Parliamentarians’ honesty in declaring expenses. A receipt is not currently required for any claim below £250, though the Senior Salaries Review Body (SSRB) has recommended reducing this to £50.

However, it seems some in the Commons do not regard the current allowance arrangements as adequate.

A recent SSRB report revealed that MPs had complained that they needed more cash for taxis, security in their offices, and staff to answer the burgeoning volume of emails.

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