NICOLA Sturgeon says allegations Boris Johnson made callous comments about coronavirus victims have “the ring of believability”.

The First Minister says claims the Tory leader shouted “let the bodies pile high” in a furious anti-lockdown rant would be in keeping with his history of “throwaway” comments and opposition to tighter Covid restrictions.

And as the Prime Minister faces a formal investigation over the £60,000 renovation of his Downing Street flat, he was urged to come clean on where the money came from.

READ MORE: Boris Johnson to be investigated by Electoral Commission over flat refurbishment

“What we have now engulfing the Prime Minister is a series of very, very serious allegations,” Sturgeon told Heart Scotland.

“Now, I am not best placed to judge the veracity of all of these – certainly in terms of his alleged comments about allowing the bodies to pile higher, I wasn't there, I can't see whether or not he made those comments.

“But unfortunately, sadly, they have the ring of believability because Boris Johnson is known to make throwaway comments, and he is known – and I've experienced this directly – to have been reluctant to take some of the necessary decisions in the handling of the pandemic.”

Multiple witnesses have corroborated the Mail’s initial reports about Johnson making the comment.

The First Minister also urged Johnson to open up on the scandal surrounding the revamp of the Prime Minister’s official residence.

The Electoral Commission announced earlier that it will launch a formal investigation into the refurbishment of his Downing Street flat after confirming there are “reasonable grounds to suspect that an offence or offences may have occurred”.

Sturgeon said: “It’s beyond me why he can't just lay out openly and transparently what the funding arrangement for that was and the fact that he's not doing that, in itself now suggests that there's something very, very murky lying underneath that.”

The SNP leader continued: “Boris Johnson is clearly not prepared himself to come forward and open all of this up so there has to be an independent process of scrutiny and investigation here. We can't have allegations like this swirling around a government, particularly in the midst of a global pandemic, without proper investigation.”

She then reflected on her own experiences of being under investigation during the Scottish Parliament’s investigation into the Government’s botched handling of harassment claims.

“I've faced allegations about breaching the ministerial code in recent months – I was cleared of those and I always was very clear I hadn’t done all of these things – but I was rightly subject to really intense scrutiny over it, because the public need to have confidence in those who are in government.”

WATCH: SNP MP told language 'not savoury' as he asks Boris Johnson if he's a liar

Downing Street announced this morning Lord Geidt, the newly appointed “independent advisor” on ministerial standards, would lead a parliamentary investigation into the funding of Johnson’s flat.

However, the Prime Minister’s spokesman confirmed he will remain the “ultimate arbiter” of whether he broke the ministerial code. Despite being the subject of the probe, the Tory leader will not recuse himself.

The No 10 spokesman said: "As the ultimate arbiter of the code, the responsible for deciding on an investigation and the drawing of final conclusions from it, rightly remains the responsibility of the Prime Minister. That's been the case under successive governments."

Johnson has denied making the callous comments about coronavirus victims.