The information commissioner has ordered the Department for Work and Pensions (DWP) to release documents that are likely to expose the widespread failings of two of its disability benefit assessment contractors.

DWP has been attempting to prevent the documents being released since receiving a Freedom of Information Act request from campaigner John Slater in December 2016.

He said the documents – if and when they are eventually released – will reveal the truth about what DWP knows about Atos and Capita.

Last month, the two outsourcing companies, which are paid hundreds of millions of pounds to carry out personal independence payment (PIP) assessments, told members of the Commons work and pensions committee that they had never met contractual quality standards on the reports their staff write for DWP.

The documents Slater has been seeking could provide further evidence of such failings, and fuel campaigners’ fears that Atos and Capita have been told by DWP to find a certain proportion of claimants ineligible for PIP.

Under the terms of their contracts to assess claimants across England, Wales and Scotland for their eligibility for PIP, Atos and Capita must provide monthly reports to DWP that cover “all aspects of quality, including performance and complaints”.

The reports include detailed “management information”, including the number of complaints made against assessors, what proportion of assessments led to claimants meeting the PIP criteria, and the average length of time taken for face-to-face assessments.

Slater, who works in programme and project management when he is not campaigning on issues around freedom of information, had asked DWP to provide copies of these reports for every month of 2016.

He told Disability News Service that the reports would provide “raw data” on the companies’ performance, before DWP “has had a chance to massage it”.

He said: “I suspect what they will show is not only that the contractors are struggling but also how bad DWP is at managing contracts.”

DWP has continued to try to block Slater’s request, initially claiming that it did not hold the information he had requested, before arguing that releasing the monthly reports would prejudice the “commercial interests” of Atos and Capita.

It later told the Information Commissioner’s Office (ICO) that releasing the information “will give rise to items being taken out of context… [and] will be misinterpreted in ways that could lead to reputational damage to both the Department and the PIP Providers”, and would “prejudice the efficient conduct of public affairs” by DWP.

It also warned ICO that the information could be “maliciously misinterpreted to feed the narrative that the Department imposes ‘targets’ for the outcomes of assessments”.

But ICO has now dismissed those arguments and has ordered DWP to release the reports, although it could now appeal against this decision to the information rights tribunal.

ICO concluded that it “has not been satisfied that disclosing the withheld information would be likely to damage the commercial standing of Atos and Capita” and “has not been persuaded by the DWP that it could not provide the necessary explanation, or context, to avoid misunderstandings”.

ICO also ruled that DWP had breached the Freedom of Information Act by initially failing to say within 20 working days whether it held the information Slater had requested.

Slater has a similar appeal being dealt with by ICO relating to management information reports provided to DWP by Maximus, the contractor that carries out work capability assessments on its behalf.

Bob Ellard, a member of the national steering group of Disabled People Against Cuts, said: “The information commissioner’s ruling that the DWP must comply with John Slater’s freedom of information request on the performance information on the PIP contract is potentially very significant for disability campaigners.

“If the DWP cannot find a way to block or dodge this request (and they will try very hard to do this) this disclosure could reveal the full extent of the calamity that the PIP contract has visited on disabled people.

“It will also reveal exactly how much the DWP has known all along about how terrible performance on this contract has been.

“We as campaigners will be able to compare what they knew about the contract with the public statements that they have made, revealing the scale of lies and disinformation put out by the DWP to the public and parliament.

“While this in itself is not likely to be enough to bring down the festering sore that is PIP, it might represent another milestone on the way to achieving the end of PIP.

“We at DPAC applaud the work done by John Slater, and wish him well in continuing to pursue this and other investigations into the DWP that he is making.”

A DWP spokeswoman said: “We have received the ICO judgement and we are currently considering our position.”