ANGUS Robertson is the latest senior figure in the SNP to condemn the “unacceptable” actions of former finance secretary Derek Mackay.

Writing in The National today, the former depute party leader stated: “Like everyone else I am as shocked and disappointed by Derek Mackay and his unacceptable online behaviour. Why he thought his conduct was acceptable, sensible or responsible is beyond me, and I say that as a friend.”

The revelations which emerged on Thursday that Mackay – a senior figure in the SNP and tipped by many to succeed Nicola Sturgeon as SNP leader and First Minister when the time comes for her to step down – had sent messages via social media to a 16-year-old boy sent shockwaves through Scottish politics.

 READ MORE: 'Totally unacceptable': Politicians shocked by Derek Mackay revelations

Mackay was forced to resign from his key Cabinet role hours before he was due to deliver the Scottish Budget in Holyrood – a task which was left to his former deputy Kate Forbes. Forbes won widespread praise for her performance – including from political opponents.

The fallout over Mackay continued yesterday when Nicola Sturgeon was accused of a failure of leadership as it emerged the Scottish Government demanded to know the “justification for publication” of a story which exposed him, as well as the name of the boy he is accused of sending hundreds of messages to.

Deputy First Minister John Swinney, who said he was “utterly stunned” by the revelations, insisted the Government had “simply asked for information to give us the veracity and the substance of the points that were being put to us”.

He told BBC Radio Scotland that when he was informed the story was going to be published, it was “the first time that I had heard any revelations of this type”.

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Mackay’s resignation came after The Scottish Sun reported he had sent 270 messages to the 16-year-old boy he befriended on Facebook and Instagram.

Mackay is reported to have called the teenager “cute” as well as offering to take him to a rugby game and out to dinner.

Both SNP and opposition politicians have condemned Mackay’s behaviour.

Interim Scottish Conservative leader Jackson Carlaw claimed there had been “collective failure of leadership” from the First Minister and SNP business convener Kirsten Oswald after the story emerged.

Yesterday, a report in the Daily Record said SNP activist Shaun Cameron, 25, had been sent dozens of unwanted messages by Mackay over a period of four years.

He claimed the MSP contacted him on Facebook after meeting him at an SNP event when he was 21, and said some of the messages were “quite suggestive” – alleging the then finance secretary had asked him in September 2017: “Got any naughty pics?”

Carlaw said: “Nicola Sturgeon, when asked yesterday in the Scottish Parliament if she had sought assurances from Derek Mackay that the story reported was an isolated incident, replied merely that she was unaware of any other potential victims.

READ MORE: Derek Mackay resigns as Finance Secretary over texting scandal

“It is now clear that no such assurances were sought from Mr Mackay by the First Minister, given there are other people coming forward.

“From the start, it seems the SNP Government has been more interested in protecting its own reputation than in the welfare of potential and actual victims.”

Carlaw said the Scottish Government and the SNP “should have already established a confidential hotline for potential victims to contact to report concerns and to receive appropriate support”.

He said Sturgeon and Oswald “both now need to respond and act with far greater urgency and understanding”.

Mackay, who came out as gay in 2013, accepted in his resignation statement that he had “behaved foolishly”. He apologised unreservedly to the teenager and his family.

He said: “I take full responsibility for my actions. I have behaved foolishly and I am truly sorry.”

Speaking at Holyrood on Thursday, the First Minister said: “Derek Mackay has apologised unreservedly for his conduct and recognised, as I do, that it was unacceptable and falls seriously below the standard required of a minister.”

An SNP spokesman said: “Derek Mackay has been suspended from both the parliamentary group and the party while further investigation takes place. In the interests of due process, no further comment will be made.”

Meanwhile, a Holyrood spokesman said the Scottish Parliamentary Corporate Body (SPCB) will investigate any potential issues relating to the misuse of facilities in connection to Mackay if any such evidence is received.