After more than two years of discussion, consultation and campaigning, regulations replacing disability living allowance (DLA) with personal independence payment (PIP) were passed into law on 5 February. Implementation will be phased from this year until early 2018.

Disabled campaigners are horrified that under last-minute changes to the PIP criteria, claimants with physical mobility difficulties will have to show they can "stand and then move" no more than 20 metres "safely, to an acceptable standard, repeatedly and in an acceptable time period" to secure the enhanced mobility component. This means claimants who can walk 20 metres reasonably well but start to struggle at, say, 30 metres, won't be eligible for the Motability scheme or support to fund a private car or taxis.

It is hard to overstate the fear engendered by these criteria. Since 20 metres is a very short distance, many current DLA claimants with significant mobility impairments, including many wheelchair users and those who depend on their Motability vehicle to travel independently, will lose their entitlement.

One of our biggest fears is of isolation and loneliness, of being housebound, since for most of us contact with family and friends depends on being able to go out. Research on the impact of the Motability car scheme by Oxford Economics in 2010 concluded: "... by enabling people to visit family and friends more frequently, Motability increased its customers' wellbeing by the monetary equivalent of up to £3.2bn in 2009".

This is exemplified by the experience of a current DLA claimant: "I had left work and was becoming increasingly isolated. Receiving DLA [higher rate mobility component] has ... transformed my life by allowing me to be part of the community again – to go to the supermarket, the cinema, visit friends."

Another claimant expresses her fears about the impact of the 20-metre rule: "I have until March 2014 left on my [DLA] higher rate mobility claim and to lose my Motability car entitlement would condemn me to being virtually housebound."

Recent research has shown that chronic isolation does real physical damage, affecting cardiovascular health and reducing life expectancy. An international study has found that involuntary loneliness carries a higher mortality risk than air pollution or obesity. Under PIP, many people face loneliness and isolation and, according to the available evidence, deteriorating mental and physical health and a shorter life expectancy.

It is extraordinary that, despite clear evidence of the negative effects of loneliness on physical and mental health, and a total lack of evidence that 20 metres is the appropriate distance to decide eligibility for support to enable independent mobility, the government plans to exclude hundreds of thousands of people with significant mobility impairments from the support they need to be independently mobile.

This makes absolutely no sense in terms of preventing poor health or reducing public spending. PIP is bad for the economy and bad for public health; it needs more thought before it is too late.