Disabled people in North East Derbyshire are now waiting almost 10 weeks when they appeal decisions about their benefit claims, after wait times almost doubled in one year.
Disability charity Scope slammed the lengthy waits as "unacceptable", and called the Personal Independence Payment not fit for purpose.
People who are denied PIP – which is worth up to £145.85 a week – or who are awarded less than they expected can ask for an internal review by the Department for Work and Pensions.
In North East Derbyshire, people face a median wait of 68 days for this initial review, known as a mandatory reconsideration, according to the latest DWP figures.
This is almost double the 36-day average reported just one year previously.
James Taylor, policy head at Scope, said: "Lengthy waits for PIP decisions mean that disabled people are going far too long without essential financial support.
"Delays in income can force disabled people to make impossible choices about what they can afford.
"Disabled people are being continuously let down by a system that is not fit for purpose. The PIP assessment needs to be overhauled to restore faith and fix the system."
Scope estimates that disabled people face on average £583 per month in extra costs. With the average wait time for a review in Britain now exceeding two months, this could leave rejected claimants facing extra costs of more than £1,000 during this initial phase.
And the mandatory reconsideration is only the first step claimants have to go through in order to appeal their case.
Since PIP was introduced in 2013, replacing the previous Disability Living Allowance, 1,080 people in North East Derbyshire applied for a mandatory reconsideration.
The DWP rejected the appeal in 86% of cases.
People who wish to fight the decision can then lodge a formal appeal with the Courts and Tribunals Service – 470 have been made against the DWP since 2013 in North East Derbyshire.
The tribunal found in favour of the claimant in 72% of appeals which made it to a hearing – a process which can take months.
Anti-poverty charity Turn2Us attributed the high success rate at tribunal to claimants being able to discuss their condition outside the "strict structure" of the DWP benefits process.
David Samson, welfare benefits specialist, said: "The appeals process is already difficult for many people to navigate. It's complicated, time critical, and stressful.
"And many of the 85% of people in the UK who are rejected at mandatory reconsideration do not go onto tribunal, which could be because the process is difficult, longwinded, and there is little support available.
"This is clearly off-putting, and many people feel a deep distrust in both the claim and appeal process. The DWP urgently needs to re-evaluate this to make it easier and quicker for claimants."
A DWP spokesperson said: "We want people to get the right PIP outcome as quickly as possible.
"That's why we have introduced a new approach to gathering evidence so that fewer people have to go to appeal, and we have recruited extra staff to help reduce waiting times."