By Alistair Grant and Hannah Rodger

DEREK Mackay, whose political career now lies in tatters, grew up in Renfrew’s Kirklandneuk estate.

The 42-year-old has previously spoken of his “slightly chaotic” family life, “with a father who was an alcoholic and didn’t treat us particularly well”.

As a young teenager, he experienced homelessness. He later became the first in his family to go to university, and was elected to Renfrewshire Council in 1999 aged just 21.

It was a brutal political training ground. Police were sometimes called to disputes in the chamber.

The ambitious young politician became the SNP council leader in 2007, and moved on to Holyrood in 2011.

There, his star continued to rise. Mr Mackay was swiftly appointed local government and planning minister by Alex Salmond, before becoming transport minister.

In 2016, Nicola Sturgeon made him Finance Secretary, one of Holyrood’s top roles.

A few years previously, the father-of-two split from his wife of 12 years, Jennifer, and came out as gay.

His ascent to the very top of Scottish politics seemed unstoppable.

But behind the scenes, he was gaining a reputation for something other than political know-how.

A former senior party staffer said it was “common knowledge” Mr Mackay was openly flirtatious with young men in the SNP.

He is said to have enjoyed nights out clubbing.

Several male party members confirmed they had received late night messages from Mr Mackay, asking what they were doing or commenting on their looks.

In one message, sent at the end of 2019 and seen by The Herald, Mr Mackay starts a conversation with a young man at 1am, before telling him he is “possibly drunk”.

He goes on to say: “That was a rather nice pic of you in the bed the other week.”

Another party member recalled a night out at CC Blooms – a popular gay club in Edinburgh – when Mr Mackay’s staff members had to ask a young man he was dancing with to step aside.

They said: “He was with his office staff, and he was dancing with this guy, who was all over him.

“He did look really young so one of the folk who was with Derek pulled him away to the side to check his age. It was a year or so ago.”

A former politician in Glasgow said Mr Mackay was rumoured to pursue young men in pubs and clubs in Merchant City.

He said: “It’s well-known. Friends tell me that he goes for the ‘twinks’.”

This is a slang reference to young gay men.

Elsewhere, Mr Mackay was a regular at the SNP’s annual conference karaoke.

But in 2017, such socialising was scaled back.

It is claimed Ms Sturgeon banned him from going out drinking during conferences due to concerns over his behaviour.

He joked at the 2017 SNP conference that attendees wouldn’t be seeing him at the pub after the event as ‘Nicola won’t let me’.

In August last year, he sent that first fateful message to a teenager on Instagram.

He had apparently never met the youngster. But when he later found out the boy was still in school and just 16 years old, the messages continued.

“And our chats are between us?” he asked on December 27. “Cool, to be honest I think you are really cute.”

Yesterday, there was widespread condemnation in Holyrood.

It was “grooming-style behaviour” and “completely disgraceful”, said Scottish Tory interim leader Jackson Carlaw.

Scottish Labour leader Richard Leonard called it “predatory”. He had “abused his position of power with a vulnerable adolescent”.

But alongside the outrage, there was something else, too: regret.

Mr Mackay was respected and well-liked, even by political opponents. Journalists found him amiable and switched-on.

“I’m dismayed,” said Mr Carlaw. “Derek isn’t someone I’ve ever had any active dislike for in politics at all.

“He’s one of those who has had an appeal across all parties on a personal basis.

“But unfortunately that cannot excuse in any way at all what is a colossal lapse of judgement on his part and the consequences that follow from that.”