The company which carries out "fitness-for-work" tests on disabled people has been told to improve its services, after an "unacceptable reduction" in the quality of its written reports.


A government audit of Atos Healthcare followed concerns being raised about the French-run firm.


Some 400 reports were analysed, with retraining and re-evaluation of staff among the measures recommended.


Atos said it provided a "professional and compassionate "service.


The company runs Work Capability Assessments, gauging eligibility for Employment and Support Allowance (ESA) and Incapacity Benefit.


It carried out one million face-to-face interviews last year and employs about 1,400 doctors, nurses and physiotherapists.


'Improvements'


But assessors have been accused of making too many mistakes and assessing people as fit for work when they are not, and many disabled people claim to have been wrongly turned down for ESA.


The quality of reports produced by Atos following an earlier assessment are graded A to C, with the number of C grades around 41% between last October and March.


Employment minister Mark Hoban said: "I am committed to ensuring the Work Capability Assessment process is as fair and accurate as possible, with the right checks and balances to ensure the right decision is reached. Where our audits identify any drop in quality, we act decisively to ensure providers meet our exacting quality standards.


"Since 2010 we have made considerable improvements to the system we inherited from the previous government. However, it's vital we continue to improve the service to claimants, which is why we are introducing new providers to increase capacity."


In a statement, Atos said: "We continue to provide Work Capability Assessments on behalf of the Department for Work and Pensions and continue to support the need to increase the number of health professionals on the ground to minimise waiting times and improve the system for those going through it.


"Our priority is the quality of our work and, following the recent audit, we quickly put in place a plan to improve the quality of written reports produced following an assessment.


"The professional and compassionate service we provide to claimants and the well-being of our people remain our primary consideration.


"We are sorry when we do not meet our own high standards but can reassure that a C grade report does not mean the assessment was wrong and there are checks and balances throughout the system so that the correct decision on benefit is made by the department."