MPs were shamed yesterday after the much vaunted opening of their expenses files produced a humiliating cover-up of the most serious abuses.

Parliament and its officials were accused of colluding in a £2 million operation to protect the greedy as the supposed new era of transparency was drowned in a sea of black ink.

More than a million pieces of paper — bills, receipts and claim forms — were posted on the House of Commons website shortly before 6am, but thousands of them were indecipherable. Much of the information was blacked out as the MPs, helped by the authorities, censored incriminating material, citing security and privacy.

The redactions included addresses, making it impossible to tell from the official version which MPs “flipped” their second homes to maximise returns from the taxpayer or changed the designation of their homes to avoid paying capital gains tax.

Even so, the exposure produced more dramatic developments in a saga that has shaken politics to the core.

It was slipped out last night that about 200 MPs had rushed to pay back nearly £500,000 because of public outrage over their claims.

In four years, Labour MPs have channelled £235,000 of taxpayers’ money to a computing consultancy that operates from party headquarters. Several Cabinet ministers have used their Commons allowance to pay Computing for Labour to manage communications in their constituency offices.

The papers revealed that Alistair Darling, the Chancellor, asked his accountants to change the wording of an invoice for tax advice before he submitted it to the fees office and controversially claimed it back on expenses.

David Cameron said that he would repay almost £1,000 in overpayments on mortgage, electricity and phone bills. He blamed the overpayment on an “inadvertent administrative error”.

The expenses scandal has already ended the careers of 20 MPs, and more are expected to follow.

The cover-up shocked campaigners. Commons officials had removed references to previously revealed absurdities such as the cleaning of moats and the purchase of houses for ducks. The names of companies providing goods and gardening services were also blanked out to avoid having to show where the work was done.

Without earlier disclosures no one would have known that Hazel Blears claimed second home expenses for three different properties in a year, or that the second home of Margaret Moran, who claimed £22,000 to treat dry rot, was in Southampton, 100 miles from her constituency.

The official record would not have exposed the Labour MPs David Chaytor and Elliot Morley, who claimed thousands of pounds against mortgages that had already been paid off. This only emerged after their addresses were cross-checked against Land Registry records.

Nevertheless, the political establishment was smarting as the full tawdriness of its claims was laid bare to a public audience. By 4.30pm, 250,000 people had visited the website and clicked on 1.5 million pages.

The receipts revealed that the Conservative MP Graham Brady claimed £71 to get back into his house after being locked out and that the former minister John Reid claimed £29.99 for a book explaining basic economics.

Tony Blair, the former Prime Minister, spent £260 on shredding as he wound up his parliamentary affairs, and claimed £6,990 for repairing the roof of his constituency home two days before leaving No 10. The fees office reduced his claim to £4,453. Others spent a fortune on paper clips, matches, milk frothers, assertiveness training courses and the Racing Post.

MPs themselves were hugely embarrassed by the cover-up.

Vince Cable, of the Liberal Democrats, said: “If people had had to rely on this information to find out about their MPs they would have been faced with swaths of black ink rather than information about the flipping of homes and the avoidance of capital gains tax. It took a huge amount of effort from campaigners, my Liberal Democrat colleagues and other independent-minded MPs to get even this much information released. It’s a shame that it is still far less transparent than it could have been.”

The Commons authorities spent more than £140,000 trying to avoid publishing the expenses before being defeated in the High Court in May last year. The process of scanning and editing all the receipts from 2004-08 has cost a further £2 million and taken 13 months to complete.

Sir Stuart Bell, of the Commons Commission, described the disclosure as unprecedented and said that it was right that information was blacked out to protect MPs’ privacy and security.

Maurice Frankel, of the Campaign for Freedom of Information, said: “The mood of the House of Commons was that they did not want any of this information to be published and, failing that, as little as possible.”

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