The swaths of black covering many of the most interesting details within MPs’ expense claims are largely the work of security- cleared contractors employed by the House of Commons to prepare the documents for release.

They were enlisted after a High Court ruling in May last year that ordered the publication of some MPs’ expenses after a three-year legal battle by journalists and freedom of information campaigners.

The ruling dismissed the Commons’ appeal against an information tribunal decision three months earlier that details of 14 MPs’ spending on additional costs allowance should be published after freedom of information requests.

“The ACA system is so deeply flawed, the shortfall in accountability so substantial and the necessity of full disclosure so convincingly established that only the most pressing privacy needs should in our view be permitted to prevail,” the tribunal found, before setting out strictly limited circumstances in which redaction would be justified.

MPs’ addresses should not be exempt except in individual cases where there was a “specific credible threat” to security, it ruled explicitly. Two months later in July 2008, Parliament passed an order exempting addresses from disclosure.

Without the addresses it is difficult or impossible to spot flipping or capital gains tax avoidance, know that an MP’s second home was nowhere near his or her constituency or that taxpayer-funded fixtures and fittings were delivered elsewhere.

The Members Estimate Committee (MEC), headed by Michael Martin, the outgoing Speaker, then drew up wide-ranging criteria for other information to be redacted before the expense claims of most MPs were finally published.

Contractors were brought in to undertake the process of scanning the documents and blacking out various details, before MPs were allowed to view their documents and request further editing.

The MEC said that the High Court and tribunal rulings related only to the 14 MPs covered by the original freedom of information requests submitted by the campaigner Heather Brooke and two other journalists in 2005 and 2006, and that further FOI requests could be made by people who wanted to know more about the rest of the 646-strong Commons.

The Publication of Allowances Claims guidance notes issued to MPs this year said that the information published would be limited to a member’s name, the allowance type, the date and value of claim, the goods or services published and the identity of suppliers providing goods or services to offices.

“Editing for the claims-based allowances was done on the principle that the following information would be made available and all other information would be removed,” the notes said.

After the contractors had done their work, MPs were then given access to their own edited claims, and “asked to satisfy themselves that the principle has been properly applied to their papers”, and encouraged to go through their claims an “look out for” information under 14 criteria, including addresses, all correspondence with the Fees Office, all comments made by Commons staff, the names of hotels used and the identity of anyone providing goods of services to MPs’ homes.

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