Disabled benefits claimants are waiting almost half a year on average to be awarded their first payment, with an estimated £300 million of vital funds being held up, research suggests.

Working-age claimants are waiting five months for a decision after applying for disability benefits, according to a briefing paper by the Institute for Fiscal Studies (IFS).

The research institute said this “likely contributes” to the link between disability and deprivation, with disabled people making up nearly half (44%) of the most deprived working-age adults in the UK.

It comes as separate research by Citizens Advice estimates that disabled claimants are waiting for almost £300 million in support because of the delays.

The Government was urged to “get a grip” on the backlog, as people increasingly struggle during the cost-of-living crisis.

The IFS research, released ahead of its annual report into poverty and inequality which is published next week, contains analysis of UK household survey data and Government figures.

It found that spending on disability benefits has risen as claims have increased – despite reforms intended to reduce costs and numbers.

Disability benefit claims have been steadily rising over the past three decades, from 2% of the working-age population in the early 1990s to 6% in 2020-21.

In the last two years, four fifths of the rise in claims were by those with psychiatric conditions, such as mental health problems or learning disabilities, as their main disabling condition.

Since 2013 the Government has been gradually replacing disability living allowance (DLA) with the personal independence payment (PIP), with the intention of reducing spending by 20%.

Despite this, spending on disability benefits has risen and before the pandemic was at around £11 billion a year – 70% higher than expected in forecasts before the reform was introduced.

Peter Matejic, deputy director of evidence and impact at the Joseph Rowntree Foundation, which funded the research, said: “Most people would be shocked to learn people living with serious health conditions are waiting on average five months for life-changing financial support, with half facing longer wait times than this.

“There is clear evidence disabled people face a higher cost of living. Delays this long are likely to have led many to go without essentials like food or basic hygiene in the cost-of-living crisis.”

The IFS said the majority of the most deprived disabled people do not receive disability benefits.

It said some people’s conditions are not of the sort or severity that the system supports, others are eligible but do not claim, perhaps due to finding the application process too difficult, while others will be waiting to receive their payments.

Citizens Advice described PIP as a “lifeline” for millions of people, but said the waiting list for an assessment stood at 327,000 people between February and April this year, with an average wait for a decision of five months.

It projects that £294 million of payments that would be awarded are being held up, forcing people into “impossible choices” as they try to get by financially.

More people are seeking help from Citizens Advice with PIP than with any other issue, with around 150 people an hour contacting advisers, it said.

Chief executive Dame Clare Moriarty said: “The Government did the right thing by targeting more financial support towards those who need it most.

“But there are still things they could be doing to get money in the pockets of people who desperately need it in the cost-of-living crisis.

“Getting a grip on the PIP assessment backlog needs to be a priority for the Government. Delays in getting money to people who’re entitled to it can wreck lives.”

Jonathan Ashworth, Labour’s shadow work and pensions secretary, said the waits were “unacceptable”.

He said: “Labour has repeatedly warned the Government over the soaring backlog of PIP claims… Ministers must urgently get a grip before even more disabled people are pushed into poverty and hardship under the Tories’ ‘Backlog Britain’.”

The Department for Work and Pensions said successful PIP claimants will receive backdated payments, and that processing times have reduced by six weeks compared to the previous year.

A Government spokesman said: “We know work is the best route out of poverty and have seen 1.3 million more disabled people move into work over the past five years with the support of our Work Coaches and Disability Employment Advisers.

“Where people are unable to work, our priority is that disabled people receive the benefits to which they’re entitled as quickly as possible.

“We introduced PIP to replace the outdated DLA system. PIP is a fairer benefit which takes a much wider look at the way an individual’s health condition or disability impacts them on a daily basis.

“Under PIP, 35% of claimants are receiving the highest possible support, compared with just 15% under DLA.”