The force appealed for anyone with information regarding the allegations made against Mr Mackay to contact them. A spokesperson said no formal “complaint of criminality” had been received, but the force was “currently assessing available information from media reporting and would encourage anyone with information to please come forward”.

Derek Mackay resigns

According to the Sexual Offences Scotland Act 2009, the offence of child grooming only applies to under-16s. However, the Children and Young People Scotland Act of 2014 defines a child as a person who is not yet 18, which has raised questions about a grey area in the law.

Scottish Conservative interim leader Jackson Carlaw and SNP MP Joanna Cherry both said Mr Mackay’s actions were tantamount to grooming, while Scottish Labour leader Richard Leonard said he had been “predatory”.

The First Minister said it was not for her to decide whether or not there should be a police investigation.

Jim Gamble, former head of UK-wide police unit the Child Exploitation and Online Protection Centre, said that Mr Mackay’s six months of online messages showed “patterns” of inappropriate behaviour.

He said the messages were “at best inappropriate and concerning”, given the age and power imbalance between Mr Mackay and the boy, while “at worst”, he said, they “indicate many of the patterns of behaviour” associated with more concerning conduct. He also said the information should be “passed to Police Scotland for them to review as a wider context”. “More information would help to develop a fuller understanding of intent,” he said.

Mary Glasgow, chief executive of Children 1st, Scotland’s national children’s charity, said the messages proved how vulnerable children were when online.

She said: “By resigning, Derek Mackay has acknowledged that his behaviour was inappropriate. Children 1st has always been clear that children and young people are vulnerable in situations where there is a significant difference in age, power and status between them and another person. Society should recognise by now that it is never acceptable to exploit that vulnerability.”

It was revealed last night Mr Mackay, whose personal life hit the headlines previously when he left his wife in 2013 after revealing he was gay, had sent more than 270 messages to the 16-year-old boy, whom he had never met, through Facebook, Instagram and by text.

Mr Mackay invited him to meet for dinner, to attend a rugby match and a rugby reception in the Scottish Parliament, with the former minister saying he would pay travel expenses to ensure the boy could attend. He also called the boy “cute” in one message, and asked for assurance that “our chats are between us”.

Mr Mackay offered his resignation as minister to Nicola Sturgeon on Wednesday night after they were approached by the newspaper that broke the story.

However, according to a spokesman for the First Minister, Ms Sturgeon had been unaware of the extent of the contact between Mr Mackay and the boy until yesterday morning, when she then, in her role as leader of the SNP, suspended his membership of the party and parliamentary group and instigated an internal inquiry.

Ms Sturgeon said it had been “inconceivable” that Mr Mackay should stay in government once she knew of the allegations. She said she would not pre-empt the outcome of the investigation and due process had to be gone through.

Asked if the police should be involved, she said: “It would be constitutionally and politically be wrong for me as First Minister to direct the police in any way.

“I could not be clearer of my view about the seriousness of this, but it is for the police to decide if they think there is anything to be investigated. That is not for me to decide.

“He’s no longer a member of my government and it would not have been an option to remain in government based on what I knew last night, and that went further this morning. These are serious matters. I have not tried in any way to minimise the seriousness of them.”

Her spokesman later confirmed she had met Mr Mackay in his parliamentary office on Wednesday night after they had been contacted by the Scottish Sun, but his resignation was not announced until yesterday morning to give Mr Mackay “time to speak to those close to him”.

Mr Mackay has a partner, and two sons, aged 14 and 11. Asked about the time gap between the resignation and the suspension, the spokesman said he would not speculate on the conversation between Ms Sturgeon and Mr Mackay, and whether or not he had revealed the extent of the messages.

He added: “He’s resigned as a government minister, he’s been suspended from the party and parliamentary group and that’s happened very, very quickly.” He was unable to say how long the SNP investigation might take.

The Scottish Government said it had retained Mr Mackay’s mobile phone and laptop, although a spokesperson stressed that the phone used to send messages was a personal one.

Derek Mackay: Finance Secretary resigns after he sent inappropriate messages to 16-year-old boy