The equality watchdog’s new chair, who is set to lead an investigation into whether Tory welfare reforms breached disabled people’s human rights, worked for the government on key contracts at the heart of those reforms, Disability News Service can reveal.

David Isaac (pictured) was appointed by the government to chair the Equality and Human Rights Commission (EHRC) earlier this year, despite concerns raised by two parliamentary committees over “serious potential conflict of interest” caused by his work as a partner of law firm Pinsent Masons.

He specialises at Pinsent Masons in providing advice on “major public and private sector UK and global commercial and outsourcing projects”, and his own profile on the firm’s website previously stated that he “leads teams of lawyers on major projects” for, among others, the Department for Work and Pensions (DWP), although the reference to DWP has since been removed.

But his appointment as EHRC’s new chair came as the watchdog announced that it was to investigate the human rights implications of DWP’s welfare reforms on disabled people.

Isaac, Pinsent Masons and DWP have previously refused to say which welfare reform projects he worked on for the government.

But DWP has now been forced to respond to a freedom of information (FoI) request that was submitted by Disability News Service (DNS) nearly five months ago, following pressure from the Information Commissioner’s Office.

The freedom of information response shows that DWP projects Isaac led on included, from July 2013, providing “legal services” for terminating the contract of the much-criticised outsourcing firm Atos to provide work capability assessments (WCAs).

The controversial “fitness for work” test has been implicated in hundreds – and possibly thousands – of deaths of disabled people, and in causing significant harm and distress to tens of thousands of others.

Isaac’s team at Pinsent Masons was also involved in legal work surrounding the appointment of the outsourcing company that replaced Atos as the supplier of WCAs, the equally controversial US company Maximus.

And Pinsent Masons was involved in providing legal services in relation to “contracts with third party suppliers for the delivery of services” connected with personal independence payment (PIP), from November 2013.

PIP is gradually replacing working-age disability living allowance, and is again at the heart of the government’s plans to cut spending on disability benefits.

It is not clear what services these “third party suppliers” were delivering, but DWP has told DNS that they were not the main contracts to deliver PIP assessments, which had been awarded the previous year to Atos and fellow outsourcing giant Capita.

PIP has already seen tens of thousands of disabled people have their support cut or removed completely, while disabled activists have described the benefit as “rotten to the core”, and have pointed to growing evidence of the “shoddy nature” of PIP assessments.

DWP’s freedom of information response means that Isaac, through his work at Pinsent Masons, has been closely involved in two areas of the government’s welfare reforms that will be examined by the EHRC inquiry.

There are also existing concerns over the voting record of Lord [Chris] Holmes, the watchdog’s disability commissioner and a Conservative peer, who voted in the House of Lords in favour of the government’s welfare reforms and cuts and will also play a leading role in the EHRC’s investigation.

An EHRC spokesman said in a statement: “This FoI request contains information relating to matters prior to David Isaac’s appointment as chair of the commission.

“The commission, the government, Pinsent Masons and David Isaac are entirely content that there is no conflict of interest and have robust procedures in place to avoid any possible or perceived conflicts of interest.

“David will not receive profit from work conducted by Pinsent Masons on behalf of government and he will not be involved in any aspect of advising government clients.

“David has already shown that he is a strong champion for disability rights.

“Tackling disability discrimination is one of his top priorities and he has robustly challenged government to raise its game and take more comprehensive action to improve the lives of disabled people so they can participate fully in society.

“This is why we believe that David will add important value to our forthcoming inquiry to examine issues related to disabled people and welfare reform, as he [does] to all our work.”

Harriet Harman, the Labour MP who chairs the joint committee on human rights, one of the two committees that raised concerns over Isaac’s appointment, said in a statement: “Thank you for drawing my attention to the FoI answer.

“The committee has nothing to add at this point but we will keep this issue under review.

“I would be grateful to be kept informed so that the committee has all the information necessary to continue to scrutinise the work of the Equality and Human Rights Commission.”