Up to 150 disability rights campaigners have been protesting outside IT firm Atos, which carries out "fit for work" assessments for the government.
Campaigners say its tests for people on disability allowances are "damaging and distressing" and have led to suicides.
Atos, a sponsor of the Paralympic Games, said it ensures its service is "professional" and "compassionate".
Protesters also targeted the Department for Work and Pensions in Westminster, where one person was arrested.
The small break-away group, including two wheelchair users, blocked the doors of the office in a "surprise secret action", UK Uncut said.
Protesters who got inside the DWP building have since been removed. The Metropolitan Police said one person was arrested for breach of the peace.
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