Secret filming of training given to doctors recruited by the private company Atos to assess whether sickness and disability benefit applicants are fit for work suggests that staff are monitored to ensure they do not find excessive numbers of claimants eligible.

The footage will trigger a new debate over whether there are fixed targets for the number of people who should be granted the new incapacity benefit – the employment and support allowance – something the government and Atos, the company hired by the Department for Work and Pensions (DWP) to conduct the fitness for work tests, have consistently denied.

The film also demonstrates the unease about the radically heightened eligibility criteria felt by some trainers employed by Atos to teach new recruits how to carry out the tests. It is now harder for some very severely disabled claimants to qualify for support. No matter how serious claimants problems are with their arms, for example, "as long as you've got one finger, and you can press a button," they would be found fit for work, a trainer explains.

Dr Steve Bick, a GP with 20 years' experience, applied for a job as an assessor with Atos to carry out the work capability assessment (WCA), and secretly filmed his training for Channel 4's Dispatches programme, which will be broadcast on Monday 30 July at 8pm. Undercover filming shows Bick being told by his trainer that he will be watched carefully over the number of applicants he found eligible for the highest rate of disability payments.

The trainer tells trainee assessors: "If it's more than I think 12% or 13%, you will be fed back 'your rate is too high.'" When Bick questioned how the company could know in advance the precise proportion of people who needed to be put in this category, the trainer replied: "How do we know? I don't know who set the criteria but that's what we are being told."

Bick asked: "So if we put 20% in, we would get picked up on?". He was told by the trainer that, in that scenario, his cases would be reviewed.

The DWP said it was unable to respond in detail to the programme's findings because it had not been shown a full transcript, but a spokeswoman said it was "nonsense" to suggest there were targets or expected results of any sort. She said assessors' results were monitored to make sure they adhered to an average, adding: "If individual Atos healthcare professionals record results considerably outside the average, their work may be audited to ensure quality. If no issues are found with the quality of work, no action is taken."

In the footage, one of the trainers admits during a session that the auditing process makes her feel uncomfortable.

"It's terrible sometimes, people having [problems with] both hips and both knees, but good hands. Terrible. And you know, we talk about modern work adaptations, but we know how it looks from the other side – there's no jobs for normal people, healthy people. But we have to think this way and sometimes you feel awful because you can't do anything for people. You can't feel sorry and give them the money just because you feel sorry for them ... you will go on targeted audit," she says.

During the assessment, Atos health professionals, who can be doctors, nurses or physiotherapists, have to award claimants points reflecting the apparent severity of their condition, with information gathered through a computer-led set of questions. The data is typed into a computer program during the 20-minute session, and patients who score 15 points are likely to be found eligible for support, although the final decision is taken by jobcentre staff. Patients who score below 15 points are not likely to qualify for benefits.

In the film, the trainer highlights to new trainees the way that the new system has been altered so it offers less support to certain categories of claimants.

"For employment support allowance, we talk about mobilising, which means being able to transfer from point A to point B either by walking, walking with aids, which is crutches, walking sticks, Zimmer frame or using a manual wheelchair. So if someone has no legs but they have good hands, they can sit and propel a manual wheelchair, they don't score anything. This is one of the toughest changes," she says. "I've recently had somebody with prostate cancer, but of course that's not traditionally treated with chemotherapy so I gave him no points. And I couldn't do anything else…. Same with breast cancer: the hormonal treatments don't count. So he was given no points, I felt very uncomfortable doing it and I didn't like doing it, but I had no way of scoring him."

Large numbers of people found ineligible for the benefit are appealing against the decision to find them fit for work; about 41% of those refused support go to tribunal and 30% are subsequently granted the benefit. There have been more than 600,000 appeals since the WCA started, costing about £60m a year.

The film also reveals Atos's lack of accountability for these appeals. The trainer explains: "Good thing for us is, even if you made the wrong decision … you never go to the tribunal. So, sort of, you won't be blamed."

An Atos Healthcare spokesperson said: "It is simply and absolutely untrue that there are targets for the number of people to be assessed as fit-to-work; neither set by the Department for Work and Pensions nor Atos Healthcare. Every person we see is assessed individually with a focus on the facts of their own case."

On Thursday, the high court granted permission to two disabled people to bring a claim for judicial review against the work and pensions secretary to challenge the operation of the WCA, on the grounds that it potentially discriminates against claimants with mental health problems.