The Prime Minister has backed a probe by his Government into civil servants working on drawing up the SNP's renewed plans for indpendence.

Rishi Sunak backed the investigation being done by Simon Case, the Cabinet Secretary and head of the UK Civil Service, into the matter - but refused to give his personal view.

Mr Case has already said that new guidance could be issued to civil servants working for the Holyrood administration within weeks.

Speaking on his visit to Scotland, Mr Sunak said: “What’s right is that, as the head of the civil service, it’s Simon Case, the Cabinet Secretary, who conducts a review of that particular situation and I think it’s right that we let that continue.”

Scottish Secretary Alister Jack last week wrote to the First Minister, Humza Yousaf, accusing him of being “simply irresponsible” by using public funds and civil service resources to produce the Scottish Government’s latest paper aimed at making the case for independence.

Mr Jack, who joined the Prime Minister on a visit to Aberdeenshire on Monday, said he stood by those remarks.

The Scottish Secretary said: “I think taxpayer money should be spent on public services in Scotland, that’s where the focus should be.

“We’re very clear about that and Simon Case has said he’s looking into it, and he’s looking into it, but it is important that that doesn’t have any political interference.”

Mr Sunak spoke out after travelling to Scotland to announce more oil and gas licensing and support for two new carbon capture projects, including Acorn in Aberdeenshire.

While there he stressed his Westminster Government was “focused on delivering for the people of Scotland”, adding that ordinary Scots did not want to see “more constitutional wrangling at this moment in time”.

He said: “It’s about bringing down inflation, easing the burden on the cost of living, it’s about the economy growing, creating jobs as today’s announcement illustrates.

“It’s about cutting waiting lists as we have got strong action to do in England and that’s what I think people would want to see in Scotland as well.

“Those are the issues that are concerning people at the moment, not constitutional wrangling, that’s what I’m focused on delivering as Prime Minister.

“I’ve always said I’m always happy to work constructively with the Scottish Government to deliver for people in Scotland, you saw that, I think, when I was last here, we announced the creation of two freeports which are great examples of doing something together which is good for Scotland, good for Scottish people, their jobs, opportunities and the economy.”

Mr Yousaf has already made clear he is “confident in our position” in terms of the Scottish Government’s independence papers, saying that it “speaks volumes” that the SNP’s opponents are “trying to shut down the debate instead of bringing forward their proposals for maintaining the union”.

The spokesman for the First Minister has also said: “The Scottish Government was elected with a clear mandate to provide the people of Scotland with the information they need to make an informed choice about their future.”