Chronically ill and disabled people are being left for months without benefits because officials are sending “misleading” letters to their GPs saying they no longer need to supply medical evidence on behalf of patients who are declared fit for work.

Campaigners and MPs have called for the Department for Work and Pensions (DWP) form letter to be scrapped after it emerged claimants appealing against a fit-for-work decision were left near-destitute after their GPs refused to provide “fit notes” because they were advised they did not need to.

Claimants who challenge work capability assessment (WCA) decisions are entitled to continue to receive employment and support allowance (ESA) worth £73.10 a week while they await their appeal hearing, but to do so they must obtain fit notes from their GPs to prove they are too ill to work.

It has emerged that ministers ordered changes to the standard-issue letter to remove references that made it clear to GPs they may have to issue a medical statement if their patient wished to appeal against a WCA decision. The DWP claims this was not intended to dissuade GPs from issuing fit notes.

Raji Hunjan, the chief executive of the advice charity Z2K, said the effect of the revised letter could be devastating. “We have seen how our clients, who are seriously ill, suddenly have zero income, become reliant on food bank vouchers and loans, and face a very real threat of homelessness.”

Z2K said one of its clients, called “Louis”, was refused a fit note by his GP while appealing against a WCA decision. He ran up rent arrears and became reliant on food banks before he was eventually able to switch GPs and get the medical statement he needed to claim benefits. After an eight-month wait, he won his appeal.

Prof Helen Stokes-Lampard, the chair of the Royal College of GPs (RCGP), said the lack of clarity over when GPs should issue fit notes could put patients’ finances and health at risk. “No GP wants that, and it only serves to threaten the long-standing trust that patients have in their family doctor.”

The WCA is hugely controversial because of widespread concern over its accuracy and reliability. Nationally, 72% of claimants who appeal against their WCA decision are successful. Z2K said nine out of every 10 WCA cases it takes to appeal are successful.

Last month, there was national outrage over the case of Stephen Smith, 64, who was deemed fit for work despite suffering from multiple debilitating illnesses, having his weight plummet to 38kg (6 stone) and being barely able to walk. Smith won his appeal after waiting 12 months for a hearing.

The standard letter, called an ESA65B, is sent automatically to the GPs of all claimants who fail a WCA and are declared fit enough to work. Until 2017 the letter advised GPs that if their patient appealed against the WCA decision they must continue to provide fit notes.

However, on ministers’ orders, the letter now states that GPs “do not need to provide any more fit notes for ESA purposes”. It does not mention the possibility that the patient may appeal, or that a fit note is needed for the patient to obtain ESA payments until the appeal is heard.

Frank Field, the chair of the work and pensions select committee, raised the issue with the then disability minister Sarah Newton in January. Newton replied that the wording was amended “to make the letter simpler and clearer”, adding that DWP communications were intended to be “clear, understandable and fit for purpose”.

Field replied scathingly that the wording was “not having the desired effect”, and urged her to revise it to make clear ESA claimants on appeal were entitled to fit notes. “This simple step could greatly ease the stress and worry that people who are awaiting an appeal experience.”

A DWP spokesperson said: “These letters simply inform GPs when a claimant has been found fit for work and are not intended to dissuade them from issuing fit notes for ESA appeal purposes, to claim otherwise is inaccurate.”

However, they hinted the letter may be changed: “We are committed to ensuring our communication is clear, which is why the wording of this letter was cleared by both the British Medical Association and the RCGP. However, we will of course consider feedback when revising the letter.”

It is unclear on what basis the RCGP agreed to the new wording as the change was agreed at a DWP stakeholder meeting for which, according to the Field-Newton correspondence, there appear to be no formal minutes.