Actor Alun Armstrong branded a disability benefit only given to people unable to walk more than 20 metres a "cost-cutting exercise", as he joined a protest against the rule.
People with multiple sclerosis (MS) and activists chained themselves to model brick houses opposite Parliament to protest against the Government's "arbitrary" 20-metre ruling.
The rule, introduced in 2013, is the main criterion used by the Government to assess if someone should get the highest level of mobility support under the personal independence payment (PIP) which replaced Disability Living Allowance (DLA).
The MS society says the rule is "stripping people of their independence" and that about one in 11 people have lost out on Government support because of the changes.
Armstrong, whose older sister Elaine has MS but has not been affected by the change, said he felt "very strongly" about the issue.
He said: "If you are someone with MS and you take the test and you can walk for 21 metres, that doesn't mean to say that you are going to be able to do that the following day.
"So you can walk 21 metres? That's not even going to get most people to the bus stop.
"For a lot of these people they are losing their independence, they are not able to live independently without a (specially adapted) car."
The 72-year-old added: "As far as I'm concerned it's just the Government using a cost-cutting exercise."
Several people with MS congregated on mobility scooters and wheelchairs chained to three model houses with a sign reading "Welcome to PIPville".
Braving the rain, they held placards reading "Govt rule means I can't leave my home" and "Down with pipdom!".
The MS Society said receiving the higher rate is usually required to access a motability car, essential for those unable to use public transport.
It estimates at least 9,400 people with MS have either lost this higher rate or, as a new PIP claimant, not qualified for it.
Deedee Morgan, who was diagnosed with MS 10 years ago, said she was told her specially-adapted car would be removed after she was assessed in January 2017.
She was in hospital suffering from a relapse when she was assessed by a nurse, temporarily coming out so it could take place.
The experience was "extremely upsetting and stressful" and she found out she was no longer eligible to keep her motability car two weeks later, deciding to appeal the decision.
The 53-year-old from Harlesden, north-west London, said: "This was quite a shock because my MS hadn't disappeared, if anything it had got worse, so I couldn't understand how I could be reassessed and found ineligible."
Ms Morgan was still in hospital months later in April when she heard her appeal was successful.
She was told the news the day before her car was due to be taken away.
Her family were going to have had to pay £6,500 on a credit card for her to keep it.
She added: "I don't think people realise the distress and the stress that people with MS have to go through just to be able to take for granted getting from A to B.
"If it was as straightforward as getting on a bus it would be different, but for many of us, we wouldn't be able to live a normal life without the support this benefit gives us."
Copyright (c) Press Association Ltd. 2018, All Rights Reserved. Picture (c) Jemma Crew / PA Wire.