At least a quarter of MPs' appeals against demands for repayment of expenses have been upheld fully or in part, it was claimed today.

The BBC surveyed 20 out of almost 80 MPs who challenged rulings by expenses auditor Sir Thomas Legg, and 19 said their demands had either been substantially reduced or overturned entirely. The other MP declined to comment.

Sir Thomas's report - commissioned by Prime Minister Gordon Brown as part of plans to ''clean up'' Westminster after last year's expenses scandal - is due to be published by Commons authorities on Thursday, along with the results of appeals to former judge Sir Paul Kennedy.

The overturning of significant numbers of findings could undermine the credibility of the Legg process, which has already come under fire at Westminster for penalising MPs whose allowance claims were within the rules at the time.

The BBC survey came as more MPs went public with the success of their appeals against Sir Thomas's demands.

Stockton North MP Frank Cook said Sir Paul had found ''nothing to suggest any impropriety'' over his purchase of a refrigerator for his London home, which had fallen foul of the Legg audit.

Mr Cook said: ''Whilst I am obviously delighted that I have been exonerated by Sir Paul Kennedy, what I find pretty disgraceful is the way in which Sir Thomas Legg has been painted as whiter than white whilst MPs have found themselves portrayed as dishonest money-grabbers on the basis of findings which, in many cases, are now being shown to be without foundation.

''Time after time I asked Sir Thomas Legg for information on the so-called 'guideline' he suggested I had breached and time after time he failed to respond, which left me with no option but to lodge an appeal with Sir Paul Kennedy, who has now written to me making clear - and I quote - 'I can find nothing to suggest any impropriety on your part in claiming as you did.'

''As well as the issue of the refrigerator, Sir Thomas also alleged at one stage that I owed nearly £1,000 in utility charges - again a claim which has apparently been dropped.

''I hope that this is the end of the matter but what I do find regrettable is that I - and some other of my colleagues - who were not in any way seeking to avoid our responsibilities have been subject to totally unjustified vilification because of way in which the review was conducted.''

Solicitor general and Redcar MP Vera Baird said her repayment demand had been overturned by Sir Paul.

''I had been asked to repay £1,279.23 of mortgage interest for 2008-09 by the Legg inquiry,'' said Ms Baird.

''The letter I have received from Sir Paul Kennedy says I have nothing to repay. I was told in that letter: 'Over the five-year period 04-09 you under-claimed by £368.73. You only claimed for payments for which you were entitled to receive that is what matters to me. It is not fair and equitable to require any repayment.'

''My name is now totally cleared and that is fair.''

After auditing all MPs' expenses between 2004 and 2008, Sir Thomas last year instructed about 200 MPs to return hundreds of thousands of pounds in ''excessive'' second home claims.

But he infuriated many by imposing retrospective rules and caps on spending on activities such as gardening and cleaning at second homes.

Among those cleared altogether were Tory MP Roger Gale, Liberal Democrat Jeremy Browne and Labour's David Clelland.