MPs can claim for fishtanks and iPods on their expenses, the head of Parliament’s finance department has admitted.

Andrew Walker, director general of resources since 1997, told a tribunal yesterday that until 2003 MPs may have been able to “write their own cheques” from their taxpayer-funded allowances. In an unprecedented glimpse into the backroom workings of the House of Commons, he said the system was overhauled in 2003 after Michael Trend, then the Conservative MP for Windsor, claimed £90,000 for a second home he did not have.

But at a Freedom of Information tribunal yesterday, it emerged that the Commons still has no definitive rule book on what can be claimed and the “Green Book” used by MPs is not intended to cover every scenario.

The three judges sitting on the tribunal began a two-day hearing yesterday to decide whether Parliament should be forced to disclose more details about the additional costs allowance, the £23,000 to fund and maintain a second home. The cases have been brought by The Sunday Times, Sunday Telegraph and Heather Brooke, a freedom of information campaigner. A verdict is expected in a fortnight.

The Commons authorities are resisting because it would “distract them or lead to additional questions which they have to defend, even if they have (acted) perfectly sensibly, because there is a great desire to look at the private lives of public individuals”. Mr Walker said that he feared MPs’ personal information might be abused by the media or others and such levels of disclosure might put people off becoming MPs.

He questioned the public interest of the Times story on Tuesday revealing that the refurbishment of the Clerk’s house cost £100,000, arguing that it fed “public curiosity” rather than fulfilling “public interest”.

The tribunal was told that the Commons has been using a secret spreadsheet, known as the “John Lewis list”, which determines whether items such as washing machines and TVs are within the limits allowed. Mr Walker was asked to produce a printout of the spreadsheet. He replied: “It doesn’t exist in paper form and whether it can be printed I don’t know.”

It also emerged that MPs can claim up to £400 a month for food without receipts, something not disclosed in any publicly available document.

Mr Walker conceded that MPs could legitimately buy an iPod from a supermarket and claim for it under the food allowance, since receipts are not required for purchases of less than £400. He also said that “a fishtank may be claimable” but he had recently turned down one request. He thought plasma screen televisions were “probably too expensive” to be claimed under the additional costs allowance.

The Derek Conway scandal, he added, showed that parliamentary self-regulation worked successfully.

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