SNP ministers have ditched long-standing plans to take over a devolved benefit for severely disabled people as they now see “no advantage” in running it in Scotland.

Severe Disablement Allowance (SDA), one of just 11 benefits devolved to Holyrood, will instead continue to be delivered by the UK Department of Work and Pensions.

The SNP has repeatedly criticised the DWP for heartlessness in dealing with benefits.

SNP Social Security Secretary Shirley-Anne Somerville is now facing questions about why she failed to tell MSPs about the U-turn in a statement to Holyrood last Thursday.

Labour said it was a “staggering omission” and typical of the SNP’s lack of transparency.

Ms Somerville, who was under fire for delaying a full devolution of benefits until 2024, did however confirm the change in a letter to UK Work and Pensions Secretary Amber Rudd.

On the same day, she wrote: “In relation to one benefit, Severe Disablement Allowance, I have concluded that there would be no advantage in transferring recipients to Social Security Scotland, and that their cases should continue to be administered by DWP.”

Ms Somerville also set out the position in an obscure document on the government website.

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The Scottish Government has been working on SDA since 2014, when it was earmarked for devolution by the Smith Commission that followed the independence referendum.

In July 2016, SNP ministers included it in a consultation on a devolved welfare system.

They said: “We will take responsibility for Severe Disablement Allowance for those people still receiving it… it will be administered by the new Scottish social security agency.”

SDA, which Scotland had been due to run from April 2020, is unique among the 11 devolved benefits as it is now closed.

Created in 1984 for those unable to work for 28 weeks in a row due to illness or disability, it was closed to new applicants in 2001.

Around 2000 people in Scotland currently receive it, 98% of them over 65, and an ‘SDA top up’ is bundled in with their state pension.

If Holyrood delivered it, this would mean a split into two payments, one from the DWP and one from Social Security Scotland.

In her letter to Ms Rudd, Ms Somerville said: “There is a small and declining caseload for SDA and there will be no new claims. The Scottish Government is not proposing to make changes to the benefit and this proposal is largely supported by stakeholders and individuals.

“I am also concerned that transferring SDA may cause unnecessary disruption to some recipients. We will seek to conclude agency agreements with DWP to administer SDA.”

Labour MSP Mark Griffin said: “While Ms Somerville was on her feet trying to spin the Scottish Parliament about the SNP’s benefits delay, she was writing to Amber Rudd telling the Tories to keep control of a key benefit for severely disabled people. Her decision to leave 2000 severely disabled pensioners at the hands of the Tories is outrageous. Carers, disabled people and pensioners are being forced to wait for change while the SNP leave new powers on the shelf gathering dust. That is a disgusting dereliction of duty. The SNP must apologise to every person in Scotland they are leaving in the hands of the Tories.”

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Scottish LibDem social security spokesperson Caron Lindsay said: “It is clear that the Scottish Government was hoping that this would go unnoticed. The Minister made a statement to Parliament but failed to update MSPs on how it would deliver this, one of 11 benefits being devolved.

“If the Scottish Government is going to stick to the ambition to create a more open, transparent social security system then it needs to drop the spin.

“The 2,000 recipients of SDA have every right to demand better.”

Ms Somerville said: “As set out to parliament, the Scottish Government becomes responsible for the payment of all devolved social security benefits from 1st April 2020.

“The Severe Disablement Allowance has not been open to new claimants for eighteen years.

“The number of people receiving the benefit in Scotland has now fallen to around 2000 and will continue to decline.

“SDA is closely interlinked with the pension system and, given that remains reserved to the UK Government, establishing a separate payment system would put claimants at risk. This is another example of why it would be easier to have full responsibility for the social security system, rather than having to work with the complex and often dated systems in place in the UK Government.”

In a separate development, Ms Rudd yesterday blamed SNP ministers for the delay in devolving all benefits to 2024, three years later than promised.

In a letter to Tory MSPs, she cited the “slow development” of detail by the Scottish Government and an “underestimating” of the work involved in building up a new social security agency and “transferring significant caseloads in a safe and secure manner”.

She said: “In order to ensure that Scottish people receive these crucial benefits, DWP will continue to deliver these benefits on behalf of the Scottish Government until their own social security agency has the capacity to deliver benefits.

“DWP remains critically dependent upon the Scottish Government to provide greater detail of their specific benefit policies and how they intend to implement them.

In a separate development, Ms Rudd also announced around 270,000 disabled pensioners would no longer have to undergo “unnecessary” repeat assessments for disability benefits.

In a speech to the charity Scope, she said it would “level the terrain” for disabled people.

“Disabled pensioners have paid into our system for their whole lives and deserve the full support of the state when they need it most. This Government, therefore, intends to change the landscape for disabled people in Britain: to level the terrain and smooth their path.”