Nigel Farage has shifted ground on an offer to allow an independent audit of his spending of European parliamentary allowances, denying he ever accepted the suggestion.

In an interview with the Guardian, the Ukip leader instead claims it would be wrong for him to be singled out for a spending audit as it would put him in a different position to every other British MEP.

Farage said it was not the case that a fortnight ago he said he was happy to have his expenses independently audited. He told the Guardian: "I said if every other British MEP wants to, then I would.

"I mean, I am not going to be one out of 73 that is held up as an example of all that is wrong with the European Union. After all, I've been saying that myself for years, so this is absolutely ludicrous. If all 73 people want to go on to a new regime then of course I'll do it, but to be singled out in this way is frankly ridiculous."

But Farage appeared to say something different when he was questioned on 15 April following allegations in the Times newspaper about the misuse of his allowances.

When asked on BBC Radio 4's Today programme if spending on his parliamentary allowance was independently audited, Farage replied: "No it is not. It does not need to be. There is no provision within the rules of the parliament for any of this to be audited."

He was then asked by the interviewer: "Would you be happy for that to happen? To say 'Yes, I will have this looked at by an independent accountant?'" to which Farage replied: "If that would settle the argument of course I would".

His new stance was challenged by the Liberal Democrat MEP Chris Davies who said almost all Labour, Liberal Democrat and Conservative MEPs commission professional accountants to audit or certify the spending of their allowances.

The audit published on MEP websites is required by all three political parties and goes beyond what is required by the European parliament.

Davies said Farage should stop changing his position.

"He has variously claimed that his receipts have been lost or that he hasn't had the time to complete his expenses. He will not account for many tens of thousands of pounds of public money given to him for office expenses over the years.

"Like the overwhelming majority of British MEPs I publish independently audited accounts for my general expenditure allowance spending. I have done this for many years and will continue to do so."

Jon Ashworth, the shadow Cabinet Office minister, also called for Farage to be open with the public. "Ukip should bring itself into line with the other political parties in the European parliament. It should have its MEPs' allowances independently audited by a professional."

When asked by the Guardian whether he could guarantee that every penny had been spent correctly, Farage said: "I can guarantee one thing; that I haven't done it for personal gain. But how I've spent my time and money, and whether I've spent it because I'm an MEP, or because I'm Ukip, I would suggest to you is a very grey area.

"It's a difficult divide. I've made no bones about it that I would use the wherewithal provided by the European parliament to go round Britain and campaign against Britain's membership of the European Union. I think I'm just about within the rules. I think I've kept just the right side of the line, albeit pushing right up to it, sure."

He said the public was not interested in whether he had spent the monthly fixed-rate allowance of £3,850 for MEPs properly.

"I mean, given the abuses for personal gain that have gone on with expenses in Westminster, I don't think the general public are that interested in whether I've strictly observed the rules on what is campaigning and what isn't. We always knew these criticisms would come at some point, but I have a completely clean conscience. If someone in Brussels wants to martyr me for that then well … well, they won't, they won't."

Davies said MEPs receive an annual allowance of £44,000 which is intended to cover the cost of rents, telephone bills and all expenditure associated with the running of an office. The money is paid into an MEP's private bank account and the parliament trusts individuals to use it in accordance with the rules. There is no requirement for receipts to be kept, although many British MEPs do so and publish details of their expenditure.

• The full interview will be published later on Friday.