Westminster's three main party leaders yesterday scrambled to get on top of the growing row over MPs employing family members at taxpayers' expense, with all of them calling for transparency and with an admission that the practice has been widely used to compensate for low MP pay increases.

In the wake of the scandal over Derek Conway, expelled from the Conservative group this week for employing at least one son while he was a student and doing no parliamentary work, his former leader David Cameron was first out yesterday morning with a damage-limitation bid.

He said a ring-round of his party's MPs found more than 70 of them employ wives, husbands or other family members - more than a third of the total 196.

He said that, as a first step, he was asking Tory front benchers to register any family member paid for out of their MP's staffing allowance from April 1.

"What needs to happen more broadly is a change of culture at Westminster," said the Conservative leader. "For a long time allowances were seen as a top-up to pay that wasn't increasing. We live in a different age where more transparency, more openness, is rightly required and MPs have to respond to that."

Gordon Brown immediately made clear he expected all Labour MPs, and not just front benchers, to identify any family members working for them: "We have said there has got to be transparency from every MP, not just one group of MPs. This is taxpayers' money. People have to be sure that the money is going to people who are actually doing the job."

Lib Dem leader Nick Clegg added to his rivals' calls for more transparency. After publishing details of his own staff on his websites, he urged to do so too, but warned party leaders cannot legally force their MPs into such disclosures.

He wants a ban on MPs employing more than one family member, as well as spot-checks on expenses claims with a requirement to produce receipts on all items over £50, rather than £250 as at present.

"There's a huge challenge for Westminster to haul itself from the 19th century into the higher standards of transparency in the 21st century," he said.

On Monday, a Commons committee that oversees MPs allowances is to consider a proposal for the National Audit Office to conduct spot checks on up to 10% of MPs to ensure their claims are genuine.

That is chaired by Commons Speaker Michael Martin who previously blocked a request from a freedom of information campaigner to publish all names and salaries of MPs' staff.

The rush to clear up the expenses scandal comes after the Commons' 10-day suspension on Thursday of Mr Conway, Tory MP for Old Bexley and Sidcup, after it was found that there was no evidence of any work being done by his son, Freddie, in exchange for salary payments of £45,000.

The MP faces another standards commissioner inquiry, referral to the police, and while he has said he will not stand again at the next general election, there is pressure for him to quit before then.

The toxic relationship between politics and money, also including a series of investigations into Labour and Tory fund-raising, is expected to step up pressure on MPs to accept their expenses regime will have to change.

In some countries, including Germany and the US, the employment of family members is banned.

The practice is used in Holyrood as well, where at least 17 MSPs employ their wives, husbands, sons and, in the case of Livingston MP Angela Constance, her mother-in-law.

One key difference at the Scottish Parliament is that MSPs' staff are directly employed by the parliament, which issues and oversees a formal contract of employment. The UK Information Commissioner, Richard Thomas, ordered the Commons earlier this month to disclose more information about MPs' spending of allowances, including on staffing.

But his Freedom of Information ruling called only for monthly staffing costs to be published, not details of each employee and their salary, and even that could yet be subject to an appeal by the Commons authorities.