THERESA May is facing calls from the SNP to shelve “devastating” cuts to welfare payments for disabled and sick people who are unable to work.

Tory ministers plan to slash Employment and Support Allowance (ESA) by £30 a week for those who are in the Work Related Activity Group (WRAG).

The payments for sick and disabled claimants in that category go from £102.15 to £73.10 from April 2017 – equal to jobseeker’s allowance – if they are deemed fit for “work-related activity”.

However, SNP MP Neil Gray has written to the Prime Minister, calling for her to “scrap the expectant arbitrary cut to payments”, which he claimed would damage the health of vulnerable claimants.

Gray, the SNP’s spokesperson for Fair Work and Employment at Westminster, challenged May to deliver on her pledges to fight “burning injustice” and take on the “privileged few”, made in her first speech after she entered 10 Downing Street in July. In his letter warning the PM about the consequences of the cuts, Gray said the welfare changes would push vulnerable people into dire poverty, as he cited a survey showing that some claimants were struggling to survive on their existing benefits.

Gray said: “Theresa May must live up to her rhetoric on social justice and inequality instead of ploughing forward with devastating cuts to support for people who have been deemed unable to work by her own government.

“Far from acting as an incentive for disabled people and those suffering from ill health, this arbitrary cut of £30 a week is more likely to push people into hardship – it is only by tackling the barriers facing people with additional needs we can truly help disabled people and those with ill health back to work.

“Tory backbenchers were promised support for disabled people in the still pending Work and Health programme. It’s time Theresa May sent a clear message that the rights of the sick and disabled people will be protected by her Government.

“The SNP Scottish Government announced new employability support programmes for disabled people with respect and dignity at their core – but with 85 per cent of welfare spending still in the hands of the increasingly right-wing Tories at Westminster, the SNP will continue to put pressure on the UK Government to reverse the damage done by their regressive social policies to the most disadvantaged in Scotland.

“It is time for Theresa May to admit that Iain Duncan Smith got it badly wrong with his welfare reforms and to abandon their ideological commitment to austerity. The new Prime Minister must immediately scrap the cuts to ESA WRAG before even more damage is done to the lives of people who are disabled and sick.”

The plea to May to abandon the cuts comes after the SNP’s social justice policy team at Westminster held talks in Edinburgh with disability organisations to gather their views on Tory changes to welfare support.

In his letter to the PM, Gray said: “This cut takes no account of the actual ability of sick and disabled people to work. I note your pledge in your inaugural speech to fight ‘burning injustice’ and take on the ‘privileged few’. These words are encouraging, however they must translate into action.

“It would send a clear message that your Government is committed to social justice and ending inequality by abandoning these devastating cuts to support for people who have been deemed unable to work by your government.”

Gray highlighted a survey from the the Disability Benefits Consortium to the PM which found that seven out of ten disabled people said that a cut in ESA would cause their health to suffer, with a third saying that they couldn’t afford to eat on the current amount they receive.

However, a spokesperson from the UK Government’s Department for Work and Pensions said: “These changes are about ensuring that people with potential for work aren’t trapped on welfare benefits. Nobody currently on ESA or those with the most severe disabilities is affected by these changes.”

The spokesperson added that the Scottish Government “now controls over £14 billion of income tax and welfare spending and has significant powers to create new benefits”.