NICOLA Sturgeon has been accused of presiding over an "astonishing" lack of transparency after her office admitted it had no standard written record of Derek Mackay's resignation.

The Scottish Government last night confirmed to our sister title, The Herald, there was no formal exchange of letters between the First Minister and the former finance secretary detailing why he quit.

Five days after Mr Mackay was last seen in public, officials said he had "resigned verbally" after the Scottish Sun revealed he had been pestering a 16-year-old schoolboy on social media.

A Government source said it was merely "custom" for there to be an exchange of letters, and there was no requirement for a Cabinet Secretary to write one or the First Minister to reply.

However opposition parties said it was highly irregular that there was no paper trail of the Government losing its second most powerful member.

READ MORE: Derek Mackay to receive £12,000 pay off after 'predatory' text scandal

Mr Mackay, 42, quit after it emerged he contacted the boy out of the blue without knowing his age last August, then sent 270 messages over six months.

The Renfrewshire North and West MSP called the boy "cute", asked him to dinner and asked that their conversations be kept secret.

Opposition parties called it "predatory" and textbook "grooming".

Mr Mackay resigned on Wednesday evening and public finance minister Kate Forbes was tasked with delivering the draft budget the next day.

Mr Mackay was given time to speak to family and friends before the Government announced his departure just after 8am the following morning.

But this was not a classic exchange of letters in which the minister set down his reasons for leaving the Government and the First Minister set down her reasons for letting him go.

Instead, there was a "statement from Derek Mackay" issued by Ms Sturgeon's official spokesman in which Mr Mackay was quoted saying: "I take full responsibility for my actions. I have behaved foolishly and I am truly sorry.

"I apologise unreservedly to the individual involved and his family.

"I spoke last night with the First Minister and tendered my resignation with immediate effect."

In the statement, Ms Sturgeon said Mr Mackay had "submitted his resignation as a government minister which I have accepted."

READ MORE: Nicola Sturgeon accused of failure of leadership after Derek Mackay scandal

But pressed by The Herald for a copy of Mr Mackay's resignation letter, the Government said it didn't exist.

Tory MSP Donald Cameron said: "The SNP Government has form for covering things up and refusing to reveal paper trails. But on this most serious of matters, the public will expect full transparency.

"It is astonishing there's no letter submitting the resignation, nor one accepting it.

"It's high time Nicola Sturgeon adopted a more open and accountable approach to this scandal."

A Scottish Labour spokesperson added: "The lack of a formal resignation letter raises significant concerns over transparency and would impede any attempt to review the nature of the resignation in the future.

"It seems that the Government is more interested in keeping the public in the dark over this very serious matter than allowing for proper scrutiny."

A spokesperson for the First Minister said: "The Scottish Government acted swiftly, decisively and entirely appropriately when the details of this issue came to light.

"Derek Mackay is no longer a minister, and his resignation took effect immediately on it being offered. There is no requirement for a letter."

Mr Mackay has been suspended by the SNP, which is now investigating his conduct. Police Scotland has also spoken to the boy and an older SNP activist pursued by Mr Mackay.

READ MORE: 'Got any naughty pics?' Derek Mackay faces fresh allegations over unwanted messages

SNP deputy leader Keith Brown said on Sunday it is "very difficult to see" how Mr Mackay could stay an MSP.

However he cannot be forced out. Scottish Liberal Democrat leader Willie Rennie yesterday urged Holyrood's Standards Committee to create a recall mechanism akin to the one Westminster has had since 2015.

If more than 10 per cent of an MP's constituents sign a recall petition, it triggers a by-election.

Mr Rennie said: "There is merit in looking at this. I want MSPs to know that serious and harmful behaviour could lead to the ultimate sanction of them losing their job.

"At the moment voters are helpless when faced with unacceptable conduct such as Derek Mackay using the offer of parliamentary receptions to try to befriend a teenager."