THE deputy leader of the SNP has said it is "very difficult" to see how disgraced former finance secretary Derek Mackay can remain an MSP. 

Keith Brown said politicians across Holyrood were shocked by Mr Mackay's behaviour.

He said he had not had any contact with the former minister since his resignation and suspension from the SNP. 

Mr Mackay sent some 270 messages to a 16-year-old boy over six months, including telling him he was cute and asking if the chats were "between us". 

Other messages offered to take the youngster for dinner and to a rugby match. 

They continued even after the teenager said he was still in school and then later said he was 16.

The messages were published by the Scottish Sun and emerged just hours before Mr Mackay was due to deliver Scotland's £40 billion Draft Budget.

READ MORE: Analysis: Does Derek Mackay scandal mark the beginning of the end for the SNP? 

He resigned as finance secretary during a face-to-face meeting with Nicola Sturgeon on Wednesday night and was later suspended from the SNP.

Appearing on the BBC's Politics Scotland, Mr Brown was asked whether Mr Mackay should continue as an MSP. 

He said: "I think it's very difficult to see how he can continue, but it is his decision."

Asked if he had ever had concerns about Mr Mackay, he said: "No. I wasn't aware of his text habits, if you like, and this communicating with people of that age – completely unaware of that and it came as a shock to people throughout the party. 

READ MORE: Teenager at centre of Derek Mackay scandal speaks to police 

"You could see the shock on people, not just the SNP but other parties as well."