Almost a quarter of all people applying for disability benefits to help them live independently are encountering serious difficulties, including delays, unfair dismissal of claims and confusion over eligibility, The Independent on Sunday has learnt. The scale of the problem with personal independence payments (PIP) means that needing help with the benefit is now the most common reason for approaching the national charity Citizens Advice charity, new figures show.

In June last year, the Public Accounts Committee described the implementation of PIP as “nothing short of a fiasco”. Figures for April this year show 11,500 people in one month went to Citizens Advice for help with the benefit in one month. This is a significant number given that the Department for Work and Pensions (DWP) recorded only 52,000 new claimants and reassessments in the same month.

PIP began replacing the old disability living allowance (DLA) in 2013 as part of Iain Duncan Smith’s welfare shake-up. In an attempt to slash the benefits bill, the criteria for receiving help became more stringent and most claimants will now be subject to constant reassessment. Since last month, almost everyone on DLA – apart from the most extreme long-term cases – has had to reapply for PIP.

The idea of the benefit is to provide financial support for disabled people who face the greatest challenges to be independent, regardless of whether they are in work. The payments range from £21.55 to £138.05 a week, depending on the severity of the condition, to help with some of the extra costs caused by long-term ill-health or disability.

In the past year, Citizens Advice received more than 100,000 queries about eligibility for PIP and more than 50,000 approaches about issues with a claim, including problems with delays. A significant number – more than 20,000 – also needed help with challenges and appeals after being turned down for the payment.

Gillian Guy, chief executive of the charity, said: “People’s ability to live independently is at risk due to PIP failures. People are experiencing problems with every part of the PIP application process, causing a huge amount of stress and anxiety for those going through a very difficult time. For too many people the system is not working. In order to fulfil its intention, the Government needs to ensure the PIP process is implemented properly and responds to people’s changing needs.”

Figures from the DWP published in June 2015 showed that delays for PIP had fallen to an average of 11 weeks for new claimants. However, Citizens Advice has evidence that some people are still waiting more than a year, and that delays to decisions have resulted in many people falling into debt and some relying on support from family members.

Shadow disability minister Kate Green said: “These figures make worrying reading. PIP can be a lifeline, helping disabled people and those living with serious illness such as cancer or Parkinson’s disease to meet the extra costs disabled people face. Yet the Government is recklessly pressing ahead to roll out the new benefit to all existing disability living allowance recipients rather than sorting out the problems that this research shows. It’s a recipe for chaos which will leave many disabled people facing hardship and distress.”

The majority of assessments in the UK – about 70 per cent – are handled by the controversial outsourcing giant Atos. Capita handles the remaining cases in Central England, Northern Ireland and Wales.

Last year, Atos famously bought itself out of a contract assessing fitness to work tests for the DWP last year following years of protests and bad headlines – including that it found terminal cancer patients fit for work. Its role in PIP contracts has also been controversial.

An investigation by the Disability News Service last month found that the proportion of disabled people stuck in the queue to be assessed for PIP was more than five times higher in parts of the country managed by Atos than those managed by Capita. Nearly a third of new PIP claimants in Atos areas – Scotland, the North of England, London and southern England – waited longer than 20 weeks for a decision, official figures from 31 March showed.

An Atos Healthcare spokesperson said: “We are sorry that anyone has had to wait for their PIP claim and we have been clear that this has been unacceptable. We have done all we can to reduce delays quickly, while also making sure that we give each individual the time they need during an assessment.”

The disability charity Scope says that, like Citizens Advice, its helpline has been inundated with calls from people struggling with PIP. Negative decisions and poor decision-making are something the service says it hears about every day.

Mark Atkinson, chief executive of Scope, said: “We’ve heard from a large number of disabled people who used to receive DLA, but did not qualify when reassessed for PIP. Many of the callers said that their assessment report didn’t resemble what happened in their assessment.

“Life costs more if you are disabled. From higher energy bills to specialist equipment – our research shows that this adds up to on average £550 per month. Extra costs payments – DLA and PIP – are a financial lifeline for disabled people.”

Clair, 32, a mother of three from Berkshire was in a serious car accident last year that left parts of her brain pushing down onto her spinal chord. She has mobility, vision and hearing problems and suffers from constant pain and nausea. She only receives £202 a fortnight in statutory sick pay and applied for PIP in July 2014. She was not given an assessment date until February this year and it was a two hour drive away. She suffers from severe motion sickness and vomited so much on the journey that it had to be abandoned and she was hospitalised for five days.

Clair was then forced to re-apply all over again and was only interviewed for it last week, when she discovered the waiting was not over: “They said the wait would be four to eight weeks, or a bit longer, which is a long time given I’ve been waiting since last year,” she said. She is due to have major brain surgery in the autumn and says the money “would make an absolutely massive difference; it would be a lifeline.”

Paralympian Baroness Tanni Grey-Thompson, who lobbies in the Lords for improvements to disability benefits, said: “Not only has the system changed, but there are new criteria, and the appeals process is more challenging. The cost of a decision being overturned because the wrong decision was made in the first place is such a waste.

“I am also concerned about the delays, and the percentage of people who are actually being transferred over [from DLA]. I think we are potentially seeing the tip of the iceberg and we are not going to know the full scale of the problems for another 12 months.”

A DWP spokesman said: “As a major new benefit still in the process of being introduced, it is only natural that PIP will generate questions from the public. We give Citizens Advice financial support to recognise the work they do helping people understand the benefits system.”

The spokesman added that “the average new PIP claimant waits only five weeks for an assessment”, though once all those in the system are taken into account, the mean wait is more than double this. He said: “We are continuing to take a gradual and controlled approach to the rollout.”

Case study: "‘I can’t use my arms or legs, but I have to face a tribunal’"

Ronny Huelin, 52, lives in Rugby with her husband, Mike, 47, and daughter, Louise, 17

“I applied for PIP back in May on the advice of a neurological specialist treating me for an extreme version of restless leg syndrome. It’s like Parkinson’s and means I’ve lost function in my arms and legs. I can’t make the bed, wash my hair or Hoover; I can’t even pick up a kettle – it’s like I’ve got no muscles. In the night my legs and arms jerk so I wake up exhausted.

“I used to work as a teaching assistant but now I can only do playground duty for six and a quarter hours a week. I have no other income. My husband was made redundant as a warehouse operative recently. My husband and daughter help, but once she’s back at college and he’s back at work I don’t know what I’ll do. PIP would mean I could afford things like lighter pans that I can lift on my own and someone to help with cleaning.