Complaints about the personal independence payment (PIP) assessment process rose by nearly 900 per cent last year – from 142 to 1,391 – apparently corroborating the results of a year-long Disability News Service investigation.

The Department for Work and Pensions figures also show that the number of complaints about PIP assessments that were upheld rose by more than 700 per cent in the same year (from 67 in 2015-16 to 545 in 2016-17).

The figures provide probably the strongest evidence yet to support the findings of the investigation carried out by Disability News Service (DNS) into claims of widespread dishonesty at the heart of the PIP assessment process.

Labour’s shadow work and pensions secretary, Debbie Abrahams, said the “huge increase” showed that the healthcare professionals who carry out the assessments must be held to account.

She said the figures were also “an absolute indictment of the Tories’ punitive assessments and the miserable effect they are having on people trying to access desperately needed support”.

The enormous increases in both complaints lodged and those upheld, between 2015-16 and 2016-17, come despite a rise of just 34 per cent in the number of PIP claims registered in the same period.

DNS only decided to begin its PIP investigation in November 2016 because of a steady trickle of emails and phone calls from disabled people raising concerns about the PIP assessment process, and who were insisting that the healthcare professionals who had assessed them had produced dishonest reports for DWP.

The new figures appear to suggest that whatever was causing this dishonesty in the assessment system appears to have become a significant problem during 2016-17.

DNS has now heard from more than 250 PIP claimants who say their assessment reports were dishonest.

They have told DNS that assessors working for DWP contractors Capita and Atos – many of them nurses – have repeatedly lied, ignored written evidence and dishonestly reported the results of physical examinations.

The figures on PIP assessment complaints were given last week to the Labour MP Stephen Kinnock by the minister for disabled people, Penny Mordaunt, in response to a parliamentary question.

Mordaunt told Kinnock that the number of complaints received about the PIP assessment process increased from just 142 in 2015-16 to 1,391 in 2016-17 (a rise of 880 per cent).

And she said that the number of complaints about the PIP assessment process that were upheld rose from 67 in 2015-16 to 545 in 2016-17 (an increase of 713 per cent).

Other DWP statistics and DNS calculations show that, in the same period, the number of PIP claims registered – including new claims and reassessments – only increased from 783,585 to 1,047,976, a far smaller rise of about 34 per cent.

Abrahams said: “These profit-making health assessment companies must recognise that their assessments are not fit for purpose, given the increase in complaints received and numbers overturned on tribunal.

“However, assessments are conducted by clinical professionals and we must be holding these clinical professionals to account too.

“I have personally heard of dozens and dozens of cases of assessment reports not marrying at all with the assessment and medical records that were supplied.

“The huge increase in complaints made and upheld about the PIP assessment process are an absolute indictment of the Tories’ punitive assessments and the miserable effect they are having on people trying to access desperately needed support.

“Labour is committed to scrapping these harmful assessments and replacing them with a holistic, person-centred approach, under our plans to ensure that, like the NHS, the social security system is there for us all in our time of need.”

Kinnock said the figures were “further evidence that the PIP system is not fit for purpose”, despite the assessment system being in place for more than four years.

He said: “While the scale of this is truly shocking, it is not in the least bit surprising, because week after week I hear from my constituents about how claimants are treated, how they are humiliated, belittled and denied basic human dignity.

“Government has been told by MPs, claimants and by disability experts that the system needs reviewing.

“Instead, they have carried on regardless with their ideological drive to remove the help which people so desperately need, so that they are able to manage the basic daily costs of living with a disability.”

A DWP spokesman was unable to offer any explanation for the huge rise in complaints.

But he said: “Complaints may be made for a variety of reasons and there is no evidence to suggest that there is dishonesty in the assessment system.

“The percentage increases in complaints which you have mentioned do not consider the number of complaints as a proportion of the overall number of PIP cases which we process.

“We are now clearing 81,000 claims each month compared with around 80,000 per month this time last year.

“Our latest research shows that 76 per cent of PIP claimants are satisfied with their overall experience.

“More than 2.4 million PIP decisions have been made, and of these eight per cent have been appealed and four per cent have been overturned.

“In the majority of successful appeals, decisions are overturned because people have submitted more oral or written evidence.”

PIP claimants who want to contribute to an inquiry by the Commons work and pensions committee into the effectiveness of the PIP assessment system, as well as the work capability assessment, have until 10 November to submit their evidence. They can also post evidence on the committee’s web forum