The tribunals – part of the appeal process when benefits are cut – see disabled people fighting to prove their medical conditions exist to keep their benefits. The system has been plagued with claims that the sick and disabled are being forced back to work and denied welfare.
Medical reports are key to many disabled people retaining their benefits, and many ask their GP for help.
Doctors now say, however, that the number asking for help has reached such a level that some GPs are refusing to provide extra information to back benefits claims, while others are charging patients for reports. GPs – who earn around £100,000 – say the Government is not paying for this extra work.
Doctors also claim the time taken to produce the reports is creating a huge additional workload.
Some patients have been charged as much as £165 for a letter, according to Citizens Advice Scotland.
Claimants who are appealing after being refused sickness benefits are advised by the Department for Work and Pensions (DWP) to submit any information which could help their case, such as letters from GPs.
Doctors say the situation is being exacerbated by the "bedroom tax" which comes into effect next month, with worried patients also asking for letters of support to help avoid housing benefit cuts, by confirming they need a relative or carer to stay overnight to help them. The bedroom tax involves a cut in housing benefit for those deemed to have spare rooms.
The issue will be raised at the British Medical Association's annual conference of Scottish Local Medical Committees (LMC) this Friday, which discusses key concerns affecting general practice.
One tongue-in-cheek motion put forward suggests setting up a new lottery to determine the allocation of incapacity benefits – as it would be fairer to patients and reduce "inappropriate" GP workload.
Dr Georgina Brown, a GP and LMC secretary for Glasgow, pointed out that doctors already routinely sent information to the DWP as part of the application for sickness benefits, which are currently being overhauled under welfare reforms.
But she said problems often arose when patients went to fit-to-work assessments which are carried out by private firm Atos Healthcare on behalf of the Government.
"Patients are complaining that either the doctor didn't look at them or they didn't feel they got a good explanation (of their decision) and are coming to us asking for letters of support," she said.
"The DWP should not be directing patients to get letters of support from the GP, because the DWP already has the information we send in. A large number of GPs are saying to patients 'we can't do these letters any more, because we don't have time to do them, we can't get them done by the time you need them and the information they are asking for has already been sent'."
Brown said around 40% of benefits appeals are successful – with some cases won using medical information submitted on headed paper from a doctor which had already been sent to the DWP, suggesting it was a "flawed system".
On the issue of bedroom tax, Brown said there were relatively few cases where it would be medically necessary for someone to need care day and night. "It is not our role to assess whether someone feels they want someone with them overnight," she said.
"There is a feeling that if the DWP has a system which is not working we shouldn't be there to prop it up – they should sort it out at the root level and fix the problems."
Brown acknowledged that GPs can charge for reports which are not part of their core NHS work.
Dianne Jackson, volunteer manager of Stirling Council on Disability, said: "Some doctors are refusing point blank to provide evidence at all, some are saying you can have a basic report which costs £10, and if you want an enhanced report it can cost you up to £85.
"Trying to help people to get benefits is becoming very, very difficult, because we need evidence basically
"It is a huge problem. When the reform was put through I don't think the Government gave any thought to the impact on medical practices."
Susan McPhee, head of external affairs at Citizens Advice Scotland, said those going through benefit assessments were often very sick and struggling on low incomes.
She said: "It really doesn't help when they have to pay an additional financial burden, which can run into three-figure sums.
"We don't blame GPs. They did not create this system and, like CAB, are struggling to cope with the additional demands it is making on them."
The DWP said claimants were advised to submit any evidence which could help their appeal, but it was not a requirement and GPs could charge for such reports.
A DWP spokeswoman added: "To assess someone's ability to work correctly, and ensure they get the support they need, we need to make sure we get all available evidence."