A test for a disability benefit is “traumatic” for applicants and needs to change, according to former work and pensions secretary Stephen Crabb.
Personal Independence Payments (PIPs) help disabled people live an independent life.
But the Preseli Pembrokeshire MP said applicants for PIPs found the test “very intrusive”.
The UK government said assessments were carried out by qualified health professionals.
In his first interview on welfare since resigning from the government, Mr Crabb told BBC Wales’ Week In Week Out programme: “Of course you do need a system of assessment when you’re giving out taxpayers’ money.
“But the way it has been done – I see this in my surgeries, every single MP in their surgery sees this – people who felt that the assessment procedure has been traumatic, intrusive, hasn’t been a comfortable experience at all. And that’s what we’ve got to fix.
“We need to have a supportive assessment process that obviously comes to the right decision about the kind of money and resource that a disabled person needs.”
Mr Crabb spoke out a week after his successor Damian Green launched a consultation on reform of the Work Capability Assessment, which is used to apply for Employment Support Allowance.
PIPs are not means-tested and are gradually replacing Disability Living Allowance (DLA).
They were introduced in 2013 and are being rolled out across the UK. Eventually, more than 150,000 people in Wales will be assessed for them.
As secretary of state, Mr Crabb scrapped plans to cut PIPs benefits and his predecessor Iain Duncan Smith resigned over those proposed cuts in the Budget in March.
However, some recipients, like 67-year-old Judith, from Ceredigion, said receiving PIPs had left them worse off.
Judith has primary and progressive multiple sclerosis and walks with the aid of a frame.
The DLA she had received for 12 years was replaced by PIPs at the beginning of 2016, leaving her £1,400 a year worse off.
“This may seem just not very much really but when you haven’t got much to start with, it is quite a difference,” she said.
A nurse with 25 years’ experience who worked for assessment company Capita until earlier this year has claimed assessors do not necessarily have the right skills when it comes to some disabilities.
He did not want to be identified but told the programme: “A paramedic is very well designed to do the job of a paramedic. Have they got a lot of experience of somebody with MS, for example?
“Perhaps somebody with a very physical condition like MS should be assessed by somebody like an occupational therapist, or physiotherapist.
“Somebody with severe mental health difficulties by a psychiatrically trained person – but that doesn’t happen.”
Capita said staff were suitably equipped and supported to carry out assessments and on-going training was provided.
The Department for Work and Pensions said in a statement: “Assessments for PIPs are carried out by qualified health professionals who combine their clinical knowledge with an understanding of the fact that not everyone with the same disability is impacted [upon] in the same way.
“Decisions are made following the consideration of all information provided by the claimant, including any supporting evidence from their GP or medical specialist.”
Week In Week Out: Why Have My Benefits Been Cut? is on BBC One Wales on Tuesday, 8 November at 22:45 GMT.