Vulnerable and disabled people are being pressured to accept unrecorded telephone “deals” paying thousands of pounds less in benefits than they may be legally entitled to, charities and lawyers have said.

The Department for Work and Pensions has been accused of making “decide right now” offers to people who have appealed against a decision to deny them benefits. In some cases the people say they were told the offer would be withdrawn if they did not accept it within minutes.

It is claimed that by making the lower offers over the phone, the DWP is trying to settle cases that could lead to payments of significantly more each year if they go to a tribunal. Around 70% of such appeals go in favour of the people who bring them.

Several charities and law firms said they were aware of more than 100 phone deal cases between them. They accused the DWP of targeting those deemed to have a strong chance of success at a tribunal over personal independence payments (Pip) and employment and support allowance (ESA). Claimants may be susceptible to accepting a lower offer because of long tribunal waits and having no income in the meantime.

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The Law for Life charity reported that it had heard from 57 claimants and 58 welfare rights advisers of cases where disabled people were telephoned and offered awards below what they could expect at appeal. The Law Centres Network, the Public Law Project, the Royal National Institute of Blind People (RNIB) and Scope also reported having clients who had received the same calls. In many of the reported cases there was no official record of the offers.

The DWP said that if someone accepted an offer they could continue to pursue their appeal, and would have any award at a higher rate backdated to ensure they did not miss out. But lawyers and charity workers told the Guardian they were aware of many cases where claimants were not told of their right to continue with their appeal, and others where they were told of their right, but were either too vulnerable to understand or felt so worn down by the process that they simply accepted.

Claimants, some with significant cognitive disabilities, receive unannounced phone calls in which they are given an offer and told they will be called back in an hour or less and asked for a decision. This occurred even in cases where a vulnerable appellant would need support or may be unaware of their legal right to take advice before making a decision. Some were given a number of days, but only when they argued they needed more time to decide.

In many cases offers appeared to have only been put in writing after the claimant agreed to the deal; a breach of typical DWP practice. There were also claims that the DWP called vulnerable claimants directly, rather than their carers or appointees.

One woman, who looks after her husband who has young person’s Alzheimer’s, said the DWP tried to call him despite express instructions to talk to her. In another case, a man with a learning disability who doctors assessed ​as having a mental age of six​ was forced to look for work after his family (who took the call on his behalf) accepted a “deal”.

The DWP changed its appeals process last year to allow for additional evidence to be gathered and taken into account so that an appeal can end if a satisfactory conclusion is reached. A spokesperson said: “We keep cases under ongoing review to make sure the claimant gets the right outcome. We know appeals take time to be heard and if a claimant provides more evidence with their appeal, then quite rightly the decision should be looked at again.”

However, claimants who spoke to the Guardian said they felt pressured to make an on-the-spot decision on a lower offer and were not told they could continue with their appeal.

One claimant said of a DWP worker who made an offer over the phone: “She was saying I have to decide right now and if I go to the tribunal I might not get anything at all, so it’s probably best to take this offer.” Another said: “I very definitely was being offered a ‘bribe’.”

RNIB said that in many cases “claimants have simply wanted to accept the offer and not continue with appeals despite being advised that the award is lower than their statutory entitlement. The reasons cited for this is usually the length of time they have waited and the stress of going through the assessment and dispute process. Some of our clients also reported feeling put under pressure by the DWP to accept the offer to settle.”

A Law Centres Network spokesman said clients were often left with the impression they had no choice, even if the reality was different. “In many cases the claimant’s condition makes such conversations inappropriate: even if DWP tell a vulnerable claimant that they can continue their appeal after they accept the offer, the impression left is of something like a ‘final offer’.”

One man, Andy, who was supported by RNIB, was offered £58.70 less a week over the phone than his statutory entitlement, which would have left him £3,000 worse off a year. While he rejected the offer and won his case at appeal, RNIB legal rights solicitor Claire Connolly said a growing number of customers were being contacted in a similar way and said: “Our evidence suggests that in most cases the offer has been lower than our customer’s statutory entitlement.”

The Public Law Project said it was working with a number of “distressed” people receiving the offers, and was considering taking legal action.

The Bristol Law Centre, which provides free legal advice to people dealing with social welfare cases, said it had seen several clients who had been contacted directly by the DWP rather than through their caseworkers, as would be considered best practice. One caseworker, Olivia Mowll, said: “I think they don’t advise disabled people of their right to seek further advice before agreeing because they know that they would feel under pressure to accept an award – to ‘bank it’ – rather than face another event [the appeal hearing] where, as far as they know, they might be disbelieved again.”