Disability charities have renewed their criticism of fitness-to-work tests after the government said almost a million people who applied for sickness benefit have instead been found fit for work.

The applicants were denied benefits after undergoing a work capability assessment carried out by private firms contracted to the Department for Work and Pensions (DWP). But disability charities said the tests were unfair and the system was failing to give people the support they needed to get a job.

The testers assessed 32% of new claimants for employment and support allowance (ESA) as fit to work and capable of employment between October 2008 and March 2013 – totalling 980,400 people, according to the figures published by the DWP on Saturday.