BORIS Johnson was under growing pressure last night to explain the funding of the lavish refurbishment of his Downing Street flat as Nicola Sturgeon warned the “stench of sleaze” surrounding his government is becoming “overpowering”.

The Prime Minister has been accused by his former chief adviser Dominic Cummings of plotting an “unethical, foolish, possibly illegal” plan to get Tory donors to secretly fund the work.

The UK Government said for the first time on Friday that the Prime Minister paid for the revamp – reported to have cost £200,000 – out of his own pocket. However, there have been calls for Johnson to explain how he obtained the money in the first place to pay for the work overseen by his fiancee ­Carrie Symonds.

The Electoral Commission has said it is still seeking answers from the Conservative Party over whether any sums relating to the work should have been declared under the law on political donations.

It comes amid a row about lobbying of ministers after leaked text messages showed Johnson promised billionaire investor Sir James Dyson that he would “fix” a tax issue for Dyson staff working to develop ventilators early on in the Covid crisis.

And the Tory government has also recently been accused of ­“cronyism” over the awarding of ­lucrative PPE contracts to firms with political connections to the party.

The SNP have called for all of Johnson’s emails, texts, and call records to be made available for scrutiny.

Sturgeon said: “The stench of sleaze that is surrounding this UK Tory government is becoming quite overpowering.

“Whether it is contracts for cronies, donations for decorating or text messages for tax breaks it is time for the Tories to put all their dealings into the public domain and let them be properly investigated.

“There are very serious allegations being levelled at Boris Johnson and his government, including by people who worked closely inside it.

“As someone who has recently been subject to far reaching inquiries and scrutiny, a thorough investigation is needed here given the range and seriousness of the allegations.

“The SNP has led calls for a full comprehensive public inquiry and that must happen immediately.”

SNP Westminster leader Ian ­Blackford added: “There must be a full and independent inquiry into this, and ­Boris Johnson must confirm that he will make available every text ­message, every email, every call – just as his former adviser is promising to do.

“There are now so many ­different parts to this Tory scandal that a ­comprehensive investigation into the workings of this deeply dodgy Tory government is the only answer.”

In a letter to the Prime Minister, Labour’s shadow cabinet office minister Rachel Reeves also called for full transparency around the funding of the refurbishment.

Conservative former attorney general Dominic Grieve – a long-standing critic of Johnson – echoed the ­demands for full disclosure, describing the Prime Minister as a “vacuum of integrity”.

“It is all smoke and mirrors. He hasn’t said when he decided to repay it or whether he has now repaid it,” he said.

“My impression is there has been constant wriggling about the source of the money for this refurbishment.”

Cummings made his wide-ranging attack in a blog post after Downing Street sources briefed newspapers that the former aide was the source of a number of damaging leaks – including text messages exchanged between the Prime Minister and Dyson.

It follows Cummings’s dramatic ­departure last year from No 10 amid the fallout of a bitter internal ­power struggle with Johnson’s fiancee ­Symonds.

Cummings also accused Johnson of seeking to stop an inquiry into the leak of plans for a second coronavirus lockdown after he was warned it could implicate Henry Newman, a close friend of his fiancee.

“It is sad to see the PM and his ­office fall so far below the standards of competence and integrity the ­country deserves,” he said.

On Friday, the Prime Minister denied trying to block the leak inquiry, saying the public could not “give a monkey’s” about such matters.

In relation to the refurbishment of the flat, Downing Street said that the Government and ministers had “acted in accordance with the appropriate codes of conduct and electoral law” throughout.