Disabled people and anti-cuts activists have scuffled with police after occupying the lobby of the Department of Work and Pensions office in Whitehall in protest against back-to-work fitness tests run by the private health firm and Paralympic sponsor, Atos.

Scores of activists staged protests outside of the central London headquarters of the IT firm Atos before moving on to the DWP, which administers the multimillion-pound contract with the French company.

Protesters are understood to have locked themselves in to areas of the DWP's Caxton House building while others, including those in wheelchairs, occupied the building's lobby and front entrance before being removed by police. Most of the protesters have now left the building but a number are still inside.

Atos has attracted fierce controversy over its involvement in the Games while contracted by the government to carry out "fitness to work" tests on incapacity benefit claimants.

Campaigners say the £100m-a-year contract from the Department of Work and Pensions to conduct "work capability assessments" is part of a money-saving drive to force people off benefits even when they may be unable to work. They claim the scheme has driven many disabled people into poverty or, in some cases, to suicide.

On Thursday, ParalympicsGB officials denied British athletes at the Games had hidden their accreditation badges at the opening ceremony, after observers noted that none was displaying the lanyard that bears the sponsor's logo.

It emerged this week that the multinational holds government contracts worth more than £3bn with 10 government departments covering a range of services. City analysts have estimated its involvement with London 2012 – it was also a sponsor of the Olympic Games – is worth £200m in revenues.

Paddy Murphy, at DPAC, described the firm's sponsorship of the Paralympics as "beyond a joke".

"They receive hundreds of millions of pounds from the government while many disabled people are being forced to live in abject poverty because of their decisions."

In a statement, Atos said: "We fully respect people's right to peaceful protest and we understand this is a highly emotive issue.

"We do not make decisions on people's benefit entitlement or on welfare policy but we will continue to make sure that service that we provide is as highly professional and compassionate as it can be. We do this through a constant programme of training and education for our staff, a rigorous recruitment process for healthcare professionals and through continual work with the government, disability rights groups, healthcare professionals and those going through the process on the ground.

"At Atos we have proudly supported the Paralympics movement for a decade. We hope people will view the Games as we do, as an opportunity to celebrate sporting achievements."

Lord Coe, the London 2012 chairman, also re-iterated his support for Atos as a sponsor at a press conference this morning. "They are helping us with accreditation and they are helping us with the recruitment of volunteers. They are helping the media with the delivery of results. They have been in the Olympic and Paralympic space for a long time. You know my view, we can't do this without sponsors. So the short answer is that I am pleased they're here. They are helping us."