The controversial system for assessing people for the personal independence payment (PIP) gives a "disjointed experience" for claimants, with many experiencing "very long delays", a review of the scheme has found.

In his first independent review of the scheme, former senior civil servant Paul Gray said it was too early to draw conclusions about the scheme's effectiveness but he called for improvements in communication with claimants and the way evidence is collected.

The document was published as the latest quarterly figures showed 208,000 PIP claims were being paid at the end of October, a 95% increase on the figure for July, but charities said thousands of ill or disabled people were still awaiting assessment.

The statistics showed that 592,900 new PIP claims and 76,300 reassessments from the old Disability Living Allowance (DLA) system were registered between April 8, 2013 and October 31 this year.

Some 352,100 new claims and 29,900 reassessments had been cleared, meaning either a decision to award or disallow the claim had been made or the application had been withdrawn.

Mark Harper, the Minister for Disabled People, said PIP was designed to "ensure support goes to those who need it most" and insisted "considerable progress" was being made to hitting the target of ensuring no one waited more than 16 weeks for an assessment.

The Gray report said: "The current PIP process gives a disjointed experience for claimants. Some short term improvements are needed, for example to communications including decision letters.

"In the longer term, there should be a more integrated, digitally enabled claims process under common branding that would improve claimant experience and effectiveness."

The review found that the way in which further evidence is collected about claimants "can be clarified and improved".

But it was "too early to draw definitive conclusions about the overall effectiveness of the PIP assessment based on available published data" and "a rigorous evaluation strategy that will enable regular assessments of the fairness and consistency of award outcomes should be put in place".

The report said the "overriding theme" in responses to the review "was the impact of delays and backlogs, with a particular frustration from claimants about knowing the status of their claim and how long they would need to wait".

There were also complaints about the complexity of the claim form, while Department for Work and Pensions (DWP) staff "highlighted constraints posed by different IT and associated systems".

The report was welcomed by charities, who said it recognised the flaws in the system and urged ministers in Iain Duncan Smith's department to "get a grip" on the backlog of claims awaiting assessment.

Richard Hawkes, chief executive of the disability charity Scope, said: "We are pleased that the review has recommended that the experience disabled people go through, and that the way additional information is collected, should be improved.

"We hope the Government adopt these recommendations, and continues to deal with its backlog of claims.

"But this review took its eye off the ball when it did not look at what the test assesses.

"There still remain fundamental problems with the assessment for PIP.

"Two people with a similar level of impairment can have very different costs associated with their disability, but the payment they receive to cover those costs will be the same."

James Bolton, policy officer at Mencap, said: "Today's official statistics on PIP are extremely worrying. Hundreds of thousands of people are waiting for an assessment.

"Although the backlog has reduced slightly, this reduction has been far too slow and is still causing considerable undue distress and anxiety to thousands of disabled people."

He added: " Gray's review recognises the serious flaws and failures in the PIP claims process - failures which Mencap has raised concerns about time and time again.

"In particular, Gray's acknowledgement that we need to move away from a 'one size fits all' model and use a more tailored approach based on the claimants' needs highlights one of many flaws that have plagued the process since its inception."

Sarah Lambert, head of policy at the National Autistic Society, said: " The report suggests ways of tinkering with the assessment process but this won't deal with the most pressing issue of the huge backlog of claimants. The Government must recognise the damage the backlog is having on people with autism and suspend reassessments immediately, until it's cleared."

Steve Ford, chief executive at Parkinson's UK, said: "Put simply, the Government needs to get a grip on PIP."

He added: "Leaving vulnerable people with Parkinson's for up to a year with the uncertainty of whether or not they'll be able to meet the mounting costs of their disability is nothing short of a disgrace."

Mr Harper, said: "Unlike the old system, Personal Independence Payment includes a face-to-face assessment and regular reviews to ensure support goes to those who need it most.

"Today's figures show just that, with nearly 22% of people getting the highest level of support, compared to 16% under DLA.

"Between January 2014 and October 2014 the number of claims processed has increased by four times from around 16,000 to 66,000 per month, and we are working hard to continue to make further improvements.

"We are making considerable progress towards the target that no one will be waiting longer than 16 weeks for an assessment by the end of the year."

The Government will formally respond to the Gray review in due course, he added.

Shadow minister for disabled people Kate Green said: "Today the Government's own review of the new Personal Independence Payments (PIP) shows that David Cameron's government is failing disabled people who try to access essential financial support, and that an overhaul of the claims process is required.

'This damning report by Paul Gray has found PIPs have been 'disjointed' and disabled people have experienced 'delays and backlogs'. It's another example of Tory welfare waste."