More than 200,000 people face being refused all or part of their disability benefit amid a "spike" of rejections, new figures suggest, prompting concerns over the accuracy of assessments.
Senior Labour MPs and a Tory are among those warning the process for assessing personal independence payments (PIP) claimants is not "up to scratch" and "pot luck".
Figures released to Parliament show 134,000 people were awarded "zero scores" on their assessments in just six months from April to October 2016, suggesting the total 2016/17 figure will surpass 200,000.
Around one in seven people assessed are now thought to be awarded zero scores for both parts of the benefit.
Claimants recently awarded zero scores and denied PIP have told the Press Association of their difficulties with the system, stating decisions have been made after just 20 minutes and benefits withdrawn despite their conditions getting worse.
The Department for Work and Pensions (DWP) said suggestions of a renewed crackdown on those looking to claim were "completely unfounded", with more people awarded higher rates on PIP than the old system.
More than 160,000 people initially denied PIP have had this decision overturned since the benefit launched in 2013, according to DWP figures.
Shadow work and pensions secretary Debbie Abrahams said: "The increasing numbers of 'zero points' assessments raise real concerns about the accuracy of the assessment process, as do the thousands upon thousands of wrong decisions that are overturned at mandatory reconsideration and in the courts."
The Work and Pensions select committee has launched its own inquiry into PIP.
Committee chairman and Labour MP Frank Field said: "It begs the question of whether mandatory reconsideration really serves any purpose, is the initial assessment process up to scratch, and wouldn't it be better to give more time for officers and better training, especially on conditions of mental health, before this is first decided."
Mr Field added that he had heard additional concerns about growing numbers of people being given zero points after quick and short assessments.
The number of points an applicant receives in their PIP assessment determines whether they are eligible for either element of PIP and, if so, whether at the standard or higher rate.
It has been brought in to replace disability living allowance (DLA).
The most recent figures, obtained through a written parliamentary question by Labour former work and pensions minister Angela Eagle, show that between April and October, 83,000 people were given zero scores in their assessments for both components of PIP.
A further 51,000 were given zero scores for either part of the benefit.
In the previous 12 months, 93,400 people were given zero scores in their assessment for both elements.
"It's a trend we've noticed about people, from usually passing the PIP criteria or DLA criteria getting fewer points, even though they've got chronic conditions that are worsening," said Ms Eagle.
"In the last few weeks there's definitely been a spike of people getting zero.
"The only way that this makes sense is if a whole load of people got DLA without deserving it, but that's never been my experience of DLA."
Analysis by the Press Association has compared the figures released to Ms Eagle with the total number of decisions made on PIP by DWP over the same timeframe.
This suggests that 14% of people assessed between April and October were awarded zero scores for both the mobility and daily living component of PIP.
This compares to 13% in 2015/16 and 8% in 2014/15.
Growing numbers of people are having their original decisions overturned by independent tribunals.
These appeals reverse a far higher percentage of cases than the DWP's own mandatory reconsideration system, which claimants must go through before appealing to a tribunal.
Ms Eagle says she has had four cases in her constituency where the reasons for rejection at mandatory reconsideration have simply been copied and pasted from the claimant's original rejection letter.
In another case one woman was falsely branded an alcoholic because information from someone else's file was copied and pasted over, Ms Eagle added.
Mandatory reconsiderations were "a waste of time", said Conservative MP Peter Bone, as he claimed most cases ended up going to tribunal anyway.
He added: "I have far, far too many people coming to my surgery who have been denied PIP who clearly should be entitled to it.
"It appears to be pot luck whether you get awarded it or not, and that can't be right."
A DWP spokeswoman said suggestions that the increase in zero scores was deliberate were "completely unfounded", adding: "In fact, 27% of claimants are now receiving the highest rate of support under PIP, compared to just 15% under the outdated DLA.
"Assessments are carried out by qualified health professionals and decisions are made based on information provided by the claimant and their GP."
The Government now spends around £50 billion a year supporting people with disabilities and health conditions, around 2.5% of GDP and more than 6% of all Government spending.
The assessments for PIP are carried out by private companies Capita and Atos.
A Capita spokeswoman said: "Our assessors are healthcare professionals and are equipped with the knowledge, skills and training to understand how both physical and mental health challenges impact a claimant's daily function.
"All assessments are carried out in line with the latest DWP guidelines, and the decision to award a benefit is made by DWP."
A spokesman for Atos added: "All decisions on awarding benefits are made by DWP."