Charities have warned that reductions to the Employment and Support Allowance (ESA) could force sick and disabled people "further away from work and closer to poverty".

More than 30 charities and three peers - including Paralympian Baroness (Tanni) Grey-Thompson - have signed an open letter to Iain Duncan Smith ahead of a key House of Lords vote.

They released polling figures showing that 1% of disabled people felt that the planned £30-a-week cut in ESA would motivate claimants to get a job, compared to 45% who said it would mean them returning to work later.

Meanwhile, charity Mind released separate figures suggesting that almost three-quarters of Department for Work and Pensions (DWP) threats to cut the ESA payments of people with mental health problems were issued incorrectly.

Using figures obtained from the DWP under the Freedom of Information Act, the charity found that 16% of people deemed unfit for work received decisions that could have led to their benefits being cut.

But Mind said that 73% of these decisions were eventually overturned with 4% having benefits cut for a period of time.

"The system is in chaos with three-quarters of referrals for sanctions wrongly issued to people with mental health problems," said Mind policy and campaigns manager Tom Pollard.

"Despite having been found not well enough to work, these individuals are being threatened left, right and centre, often unjustifiably.

"There is a complete lack of evidence to show that stopping, or threatening to stop, someone's financial support is an effective approach."

Mind joined other members of the Disability Benefits Consortium - including Mencap, Macmillan Cancer Support and the MS Society - in signing the open letter to protest against Mr Duncan Smith's plan to cut £30 a week from new claimants in the "work-related activity group" (WRAG) - WRAG group of ESA in order to bring it in line with Jobseekers' Allowance.

The letter warned the change would "undermine (the Government's) commitment to halve the disability employment gap and push sick and disabled people further away from work and closer to poverty".

They cited a poll suggesting that 71% of the public believe welfare cuts will make the UK a worse place for disabled people to live, against 6% who thought Mr Duncan Smith's Welfare Reform and Work Bill would make it better for them.

More than a quarter (28%) of ESA claimants said they sometimes could not afford food and 38% heating under current arrangements and 69% said they would struggle to pay their bills if support was cut.

The DWP said that fewer than 1% of ESA claimants are sanctioned in any given month, and that overall the number of sanctions fell by 21% last year.