Prospect welcomed today's demonstration by thousands of disabled people who marched to Westminster to lobby their MPs and protest at government attacks on benefits under the umbrella of the Hardest Hit alliance.

However, the union has spoken up against some groups who are targeting the private organisation contracted to carry out healthcare assessments.

Prospect national secretary Geraldine O'Connell said demonstrations being held this week outside the buildings of ATOS Origin were hitting the wrong target. The union represents 135 medical professionals employed by ATOS Origin to carry out assessments of benefit claimants.

O'Connell said: "The criteria for deciding who qualifies for these benefits are set by government policy and not by ATOS Healthcare.

"Our members are wrongly taking the flak because people think they are able to determine who gets benefits. But they do not make decisions on claims."

Assessments of claimants are carried out in accordance with descriptors to assess the level of disability that they may suffer. These descriptors are determined by the Department for Work and Pensions, stressed O'Connell.

She said the medical professionals conducting assessments simply scored points against each of these descriptors, using the principles of evidence-based medicine to provide logical and impartial advice.

Prospect warned last October that a target for ATOS Healthcare professionals to see 10 or more people a day was unrealistic, especially in the case of people with complex conditions such as stroke victims, sufferers of multiple sclerosis or Parkinson's disease.

"Any protest should be directed at the DWP and not ATOS Healthcare - where members are simply acting according to the instructions issued by DWP," said O'Connell.

The Hardest Hit campaign says many people are living in fear of huge cuts to essential benefits including Disability Living Allowance (cut by £2.17bn) and Employment and Support Allowance (cut by £2bn).

Government proposals include:

• cutting 20% from the DLA budget by replacing it with a new Personal Independence Payment
• taking mobility payments away from disabled people living in residential care and children going to residential schools
• cutting off payments of contributory ESA after a year to people struggling to get back into work due to disability or serious illness.

TUC general secretary Brendan Barber said: "Today's march underlines just how much some of the most vulnerable members of our society have been hit by deep spending cuts that have forced the Bank of England to downgrade its growth forecasts.

"The cuts are hurting but they are not working."