Two private firms of accountants are being called in by the commons to advise MPs how to set up an expenses system that would have credibility with the public.

The intention is included in a report from the Members Estimates Committee chaired by speaker Michael Martin tasked with cleaning up Parliament's image.

It was published at the same time parliamentary standards commissioner John Lyon confirmed he is investigating allegations that Martin claimed his wife's £4.000 taxi bill for shopping trips, with the TaxPayers' Alliance claiming this meant it was 'inappropriate' for him to continue in charge of the committee's 'root and branch' review of the MPs' allowances system.

A commons commission spokeswoman said she could not disclose the names of the firms that were being called in for meetings with the committee, whose hearings will also included representatives from the NAO and Revenue and Customs and the Audit Commission.

One option raised in the report, which is to form the basis of a consultation exercise, is for the NAO to carry out a detailed annual regularity audit of a random sample of 5-10% of MPs.

The NAO already audits the commons authorities but does not seek to go
'behind the members' signature' certifying his claim. Nor do commons officials. The existing principle is that MPs are responsible for identifying, claiming and certifying their own expenditure.

The report also raised the possibility of treating MPs in the same way as small businesses, with accounts professionally audited, and returns to Companies House.

Another suggestion was that they should be treated as non-executive directors.

The report warned MPs that HMRC are considering withdrawing an extra-statutory concession allowing them to charge for limited travel between Westminster and constituencies for spouses without facing a tax charge.