SNP deputy leader Keith Brown has been accused of bullying an independent watchdog after questioning the body’s scrutiny of a Government agency.

He informed Audit Scotland that its inquiry into the new multi-billion pound social security agency had been “intrusive” and claimed the scrutiny body’s work can be “onerous” and “counter productive”.

Brown, whose MSP partner is part of the social security ministerial team in the Scottish Government, also wanted to know how much the probe had cost the taxpayer.

Social Security Scotland was established in 2018 in order to administer the 11 benefits devolved to Holyrood following the independence referendum. Once fully implemented, the new agency will be responsible for billions of pounds of welfare payments to nearly 1.4 million people.

However, although the first wave of benefits has been devolved, the Government has run into problems on the next tranche.

Audit Scotland, which is accountable to the Parliament, not the Government, recently published a report which flagged up some of the problems.

The watchdog warned: “The Scottish Government does not yet have a clear understanding of the key things needed to deliver all remaining benefits in the way it intends. This includes not monitoring and reporting on how much it will cost to fully implement all the benefits.”

Caroline Gardner, who as Auditor General is the most senior official in the watchdog, gave evidence to a Holyrood committee last month to answer questions on the report.

Brown, who was an SNP Cabinet Secretary until last year, outlined a series of concerns about the watchdog.

“I have heard accusations that inquiries like this done by the Audit Commission [sic] are onerous. You’ve mentioned at the very start that this agency is working 'flat out', you’ve just said about all the work that they have to do, and yet they are also having to respond to what seems to be a fairly intrusive inquiry."

He continued: “It would be interesting to know what the cost of your inquiry is, whether it is in addition to any internal audit functions which the agency has, which is on top of any external audit functions.

“It would be interesting to know whether those concerns expressed by people about the role of the Commission [sic] - especially at this stage, in the early part of the development of this process - is appropriate and proportionate.”

Gardner defended the timing of the probe by saying that auditors are sometimes accused of “coming along after the battle and bayoneting the wounded”. She added that the social security powers are a “significant part of the new devolved powers”, and so providing assurances is “worthwhile”.

Brown, who also used to be Transport Minister in the Government, continued: “I know a number of transport projects, ongoing transport projects, that you’ve been involved in, as they have been going on. My concern really is that the work that you do and the demands that you place on the bodies that you are investigating, at the time when they are trying to get these things running, can be very onerous and actually counterproductive to actually delivering the service.”

He added: “There seems to be an awful lot of times when you get involved during the early parts of projects or initiatives rather than waiting to see what has happened and then looking at value for money.”

In Nicola Sturgeon’s Government, Shirley-Anne Somerville is the Cabinet Secretary for Social Security and Older People. Christina McKelvie, who is Brown’s partner, is the junior Minister for Older People and Equalities.

Scottish Tory MSP Donald Cameron said: “All things considered, Keith Brown should have thought twice before launching this tirade. It speaks to a wider problem within the SNP.

“Its arrogance after 12 years in power makes it think it can bully independent agencies, even highly respected ones like Audit Scotland. That’s a disgrace, and is yet another example why the nationalists need to be turfed out of office.”

Scottish Liberal Democrat social security spokesperson Caron Lindsay said: “It’s bizarre to see the SNP deputy leader arguing for less scrutiny of major projects. Audit Scotland are widely respected for their independent and authoritative reporting. Keith Brown would be better asking why so many SNP projects do not deliver the benefits that were initially promised.”