The firm hired to re-assess more than one million benefits claimants has been ordered to remove claims about staff numbers from its website after a watchdog judged them misleading.

Atos was also told to take down wording that said it carried out 800,000 face-to-face medical assessments every year.

The Advertising Standards Authority found it had not substantiated the claims. The French firm, which is paid £100 million a year by the Coalition Government, has faced criticism from campaigners because of the high number of decisions overturned on appeal.

The Herald revealed earlier this year that more than 30 people who were told they were fit to work had died while waiting for their cases to be heard.

Politicians have also been told that tribunal centres across the UK, including in Scotland, have been forced to hold Saturday sittings to deal with the high number of disputed judgments. In its findings, the ASA said Atos had an apparent disregard for the rules.

It judged that since Atos had not substantiated the claims, they were misleading. It ordered the firm not to put them on its website again.

The row centred on three claims – that Atos processed more than 1.2 million referrals for medical advice a year, that it completed more than 800,000 face-to-face medical assessments, and that it had more than 1700 healthcare professionals.

In its findings, the ASA said: "We considered the claims had not been substantiated and concluded the advert was misleading. It must not appear again in its current form."

It added that the ASA "was concerned by Atos's lack of response and apparent disregard for the Code", adding: "We reminded them of their responsibility to respond promptly to our enquiries in future."

More than 1.5 million incapacity benefit claimants will be re-tested in plans to cut billions of pounds from the welfare bill. Official statistics suggest that one- third of those assessed are being told they are fit to work.

However, almost four in 10 cases are overturned on appeal.

Tomn Greatrex, the Rutherglen and Hamilton West MP, said the assessment system was "mired in continued chaos".

He said: "It is wrong for Atos to attempt to gloss over its awful performance by describing its own work in such glowing terms, and that is why the ruling by ASA is welcome."

Incapacity benefit is in the process of being phased out over the next few years, to be replaced with a new employment and support allowance (ESA).

Atos was unavailable for comment last night.