The Government will roll out its re-designed disability benefit across the country today, replacing what it calls an "outdated" system.
The Personal Independence Payment (PIP), which was trialled in the North of England in April, replaces Disability Living Allowance (DLA) for working-age claimants, which was introduced over 20 years ago.
Ministers claim the new system will support disabled people to live independent lives. It includes a new face-to-face assessment and regular reviews, of a claimant's ability to wash, dress, cook and get around as well as reading and communicating.
Esther McVey, the Conservative Minister for Disabled People, said: "Disability Living Allowance is an outdated benefit introduced over 20 years ago and was very much a product of its time.
"The Personal Independence Payment has been designed to better reflect today's understanding of disability, particularly to update our thinking on mental health and fluctuating conditions.
"We are introducing a new face-to-face assessment and regular reviews - something missing in the current system. This will ensure the billions we spend on the benefit give more targeted support to those who need it most."
The PIP will now being rolled out across England, Wales and Scotland, although some existing working age claimants will start to be re-assessed from October.
When DLA was introduced in 1992, it covered 1.1 million people, at a cost of around £3 billion. That has since risen to more than £12 billion a year.
But critics say the reform doesn't deal adequately with the cost of living with a disability, and are worried about the quality of assessment.
Richard Hawkes, chief executive of disability charity Scope, said in April: “In 2013 disabled people are struggling to make ends meet. Life costs more if you’re disabled. But this year living costs are spiralling and income is flat-lining. Disabled people are getting into debt to pay for essentials.
“What’s the Government’s response? It is cutting a financial life-line for disabled people, which helps them meet the extra costs of day-to-day living when you are disabled. The reform is fundamentally flawed.
“DLA needs reforming and could be better targeted to meet the extra costs people face. But disabled people are frightened by the Government’s plans. They believe it’s just an excuse to cut their support.
And Mark Lever, Chief Executive of The National Autistic Society, said: "The national roll-out of PIP is deeply concerning. Before anyone had even walked through the door to take the new test, the Department for Work and Pensions had already suggested that successful claimants would drop by 600,000 and spending would fall by a fifth. It smacks of a cost-saving exercise, when it should be a genuine drive to make the system fairer and deliver support to everyone who needs it.
"Autism is a complex disability and the new face-to-face assessments will not be fit for purpose for many unless assessors have the training they need in the condition. Assessors for other benefits don’t appear to be receiving this training and there’s no clear indications that they will here either."
In the past decade, the number of people claiming DLA has risen by almost a third from 2.4 million to 3.3 million.
New claims will now be treated under the PIP system, before current DLA claimants start moving to PIP in October if their circumstances change or an existing claim ends.
But it will be two years before most existing claimants begin moving to PIP.
Some welfare campaigners have warned that a number of people who would qualify for the existing DLA will not meet the criteria for the PIP.