THE SNP has been accused of “getting their knickers in a twist” after claiming a UK Government minister is “undermining the devolution settlement” for her two-year long refusal to appear before a Holyrood committee.

Holyrood’s Social Security Committee will pen yet another letter to Westminster's Work and Pensions Secretary, Therese Coffey, after she has refused again to give evidence to MSPs.

Holyrood politicians have been attempting to persuade Ms Coffey for two years to give evidence to the committee – with Scotland and UK authorities both responsible for certain parts of benefits.

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In a letter to the committee, Ms Coffey said that “where matters are devolved, Scottish ministers are accountable to the Scottish Parliament” while stressing “it is for the UK Parliament to undertake this role in holding UK ministers to account”.

She added: “I have been happy for my officials to appear before the Committee where a DWP perspective is helpful.

“I remain happy to identify the best suited person to attend committees, where appropriate, going forward.”

The committee convener, SNP MSP Bob Doris, said Ms Coffey’s attitude “totally ignores the shared space and inter-connectivity between the Scottish and UK social security systems”.

He added: “This committee is not an arm of government – this committee is to scrutinise all aspects of social security in Scotland without fear or favour – be that Scottish Government officials, UK Government officials, Scottish Government ministers or UK Government ministers.

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“It’s also not for a Secretary of State to tell us who they are happy or not happy to have appear at committee – it's for this committee to best decide how to scrutinise.”

Mr Doris said that Ms Coffey’s “tone and the message” ties in to wider concerns of “undermining of the devolution settlement” and suggested the committee should write to her “insisting with all great courtesy that she comes to our committee to attend an evidence session”.

But Conservatives warned that Ms Coffey’s attitude is being misinterpreted.

Jeremy Balfour stressed that “it does come down to interpretation”.

He added: “What I view that as saying is that it is up to us to go back to the department to say what do we want to discuss with them and then they will decide which is the appropriate minister that will come to give that evidence.

“If we are talking about disability that would be a certain minister, if we are talking about Universal Credit that would perhaps be a different minister.

“I think the ball is back in our court on this. I think we as a committee need to work out what are we wanting to discuss with the UK Government – then we go back and ask the Secretary of State to identify the appropriate individual to give that evidence.”

Fellow Tory MSP, Rachel Hamilton, claimed the response showed Ms Coffey is “more than happy to discuss matters on particular issues”.

She added: “I’m not quite sure what everyone’s getting their knickers in a twist about?

“It would just be churlish to respond in a way that was inappropriate.”

But SNP SMP Keith Brown insisted the committee should go over Ms Coffey’s head and instead bring up wider issues with UK Government Cabinet Secretary Simon Case – warning her absence has been “even more explicable” given she could appear remotely.

He said: “The idea that we have to try and interpret the third paragraph to find some hidden meaning is just a nonsense.

“There is quite clearly a determination on the part of the Secretary of State not to talk directly to the parliament.

“We often hear that there are two governments in Scotland, and they must work together. Well this is an invitation to work together that has been repeated ad nauseam for two years and we’re still getting this kind of response. I think it’s completely disrespectful.”

He added: “The fact that the Secretary of State is running away from this once again is very concerning. I don’t think further letters are going to make any difference.

“I don’t think there’s any intention on this Secretary of State or most other ones to properly engage with this parliament. We need to call it out.”