LONDON — Britain’s physically and mentally challenged athletes are preparing to take on the world at the Paralympic Games opening in London this week. But across this host nation, disabled citizens are also rallying against an opponent closer to home: the government.

Headed by a Conservative-led coalition on a fiscal crusade, Britain has fully entered the age of austerity in which governments across much of Europe have made dramatic cuts. As a result, advocates here are decrying what they describe as the harshest gutting of aid to the disabled since the “golden age” of independent living in the 1970s, 1980s and 1990s, when ramped-up benefits began offering them an exit door from assisted-care homes.

Hundreds of thousands of disabled Britons are seeing their benefits cut or facing the prospect of diminished or eliminated aid. More than 15,000 unemployed disabled people a week are being reassessed by a contractor to determine whether they are fit to work. New, stricter guidelines mean that Britons who can roll themselves more than 200 yards in a wheelchair or read Braille could be considered able-bodied enough to find a job.

At the same time, the government is sending letters to nearly all disability beneficiaries, including those gainfully employed, warning that they will also soon need reassessments for other types of aid that help them cover a variety of costs, including home health-care workers and wheelchair-accessible cars.

By 2015, the government anticipates a 500,000-person reduction in those receiving Britain’s primary disability benefit. The number of claimants now stands at 3.4 million, up threefold since 1992. The vast majority of recipients, officials note, have gone on benefits without ever having face-to-face assessments to test their level of need.

“It is a gauge of your capability,” Britain’s Work and Pensions Secretary Iain Duncan Smith told London’s Telegraph newspaper, referring to the reassessment requirement to substantiate disability claims. “In other words, do you need care? Do you need support to get around? Those are the two things that are measured. Not, ‘Have you lost a limb?’ ”

But rage over the changes is running so high among disabled Britons that a week of protests has been planned to coincide with the start of the Paralympics here Wednesday.

“The irony of all this happening around the Paralympic Games is extraordinary,” said Tara Flood, 46, a former Paralympics swimmer and gold medalist for Britain at the 1992 Barcelona Games. Flood, who was born with shortened limbs, received an official letter a few weeks ago warning of a pending reassessment, leaving her “terrified,” she said, of losing the $512 in aid she receives monthly to cover the cost of her car, which she drives to work.

“I would argue this is not about trying to get disabled people back into employment or off aid,” she said. “This is simply about going after a group of people the government has now decided is too expensive in these times. They are using the kind of ‘burden on society’ argument that is dehumanizing us. We have not seen this kind of talk here since the 1970s.”