MOST cops have chased gangs.

John Carnochan has been chased by them.

The veteran detective is grinning as he remembers. Because times have changed so much since the days when the police had running battles with teenage territorial fighters.

We're walking across playing fields in Glasgow's Easterhouse. "This was like the front line," Carnochan says, pointing through rusting steel goalposts. "This was where they came to fight."

He's still smiling as he turns his head away from rain spitting through the low, bright spring sunshine.

A boy on a trail bike is buzzing across the football pitches, leaving thick black tire tracks on the sodden surface.

"That must be annoying," he says, following the biker with his eyes. "But this place used to be so much worse. It is unrecognisable."

Back in the mid-1980s Carnochan was a detective sergeant in Easterhouse. His job was to catch violent men. But sometimes he had to help his uniformed colleagues keep some kind of order on the playing fields. He remembers: "One time we got a Code 21 - officer requires assistance - and there was a cop on the pitches who had caught a boy; he was surrounded by other boys who were trying to rescue their pal.

"So we dived out of our car and chased them up there," he points on to

Aberdalgie Road. "When I got in the houses they were waiting for me, more of them, in their mid-teens. That is when they turned on me."

Carnochan was quick on his feet- he'd been a physical training instructor at the police college - not long before. He outran the mob.

Scroll forward 30 years and it's hard to imagine any of the gangs of Easterhouse - a scheme that, unfairly, became a byword for Glasgow's territorial violence - taking on the police.

As Carnochan talks, I watch walls and pavements for tell-tale tags or menshies of the Drummy and other gangs, the Young Den-Toi, the Skinheads, the Aggro. There not there. Even on the goalposts.

Carnochan, at least in my view, is part of the reason why.

Because more than a decade ago, the then Detective Chief Superintendent, spearheaded something called Violence Reduction Unit, initially focusing on issues like territorial violence in places like Easterhouse. The result? Peace, of sorts, in the schemes.

Violence is down across the northern hemisphere, not just Glasgow.

But it is dropping particular quickly in Scotland.

Take the simplest and most internationally comparable measure of violence: murders.

Well, homicide figures fell a highly creditable 32 per cent in England and Wales between 2004-05 and 2013-14. They dropped an historic 57 per cent in Scotland.

Next month Carnochan publishes his first book, Conviction, telling the story of the unit. He admits, even in the early 2000s, he hadn't given any thought to why Scotland was quite so violent. And he didn't have any idea crime could fall so much.

"Looking back I can see that I had been so busy fire fighting I had not taken any time to consider how the fires started or even why there were so many of them," Carnochan writes in Conviction. "I never consciously thought about why there was so much violence. I just presumed that's what it was like and that it was my job to deal with it."

So what changed that? Well, the old chief constable of Strathclyde Police, Willie Rae, asked Carnochan to write up a report on how to cut Glasgow's homicide rate. Carnochan, in turn, sought the advice of the force's chief analyst, Karyn McCluskey.

"We didn't have a plan," Carnochan explains over black coffee at the back of a chip shop in Easterhouse's Shandwick shopping centre. "We just knew - instinctively - that what we were doing was wrong. We can't just use jail to get us out of this problem. It doesn't work."

Rae agreed. Carnochan remembers the moment: "The chief said: "You need to lock three or four smart people in a room and don't let them out until you have a plan. So go and find two other people and a room'."

What months later emerged from that room - a windowless "dunny", says Carnochan - was the VRU, a decision by the police that they couldn't fix violence on their own. They needed teachers, doctor, nurses, dentists, social workers, community activists, everybody.

Carnochan believes this simple concession may have just been the most powerful message of all. "It was summed up in a headline on one of your stories," he tells me, "when I said I would rather have 1000 more health visitors than 1000 more police officers."

The line, splashed on the front page of The Herald, came just before the SNP came to power - partly on a ticket of boosting the size of the police force. I thought it might be controversial. I was wrong.

"You phoned me up and said can I use that line," Carnochan remembers. "Then you went rang around the Police Federation and other bodies to try and get somebody to say that was a rubbish idea. And none of them would." It was a sign policing had changed.

Now retired and able to speak more freely, Carnochan is even clearer that more cops doesn't mean lower offending. "It is a difficult thing to say having to be a cop for 40 years," he says, "but there is little evidence of a direct correlation between police numbers and the level of crime."

Scotland did get 1000 extra officers and kept them even as budgets tightened. But the SNP also scrapped Labour's "War on Neds", a crackdown on youth offending most justice experts thought was failing.

His voice grew in weight. "It was because I was the grim-faced detective," Carnochan says. "So I could talk about how the the look on the face of a parent of a son who has just been murdered is the same as the look on the face of a parent who son has just gone to jail for murder."

There followed a growing variety of schemes, including the now ended CIRV, which offered ways out of gangfighting for teenagers in places like Easterhouse.

Carnochan and McCluskey focused on "early years", interventions in schools and social work on the young boys who one day could grow in to violent men. The crime figures kept falling. So too did hospital admissions for violent injuries.

So what next, I ask. "We need to start thinking seriously about redemption," replies Carnochan. "I know that sounds like an ecclesiastical, but it bloody ain't."

Despite his passion for early years interventions, Carnochan baulks at the idea that there are people, boys, who can be written off just because they have offended. "It's never too late," his voice sending ripples through his coffee. "There is a notion that we think if we don't fix it in early years then we can't fix it. Not true.

"If same guy gets a breach or minor assault when he is 17, why does that stop him emptying bins when he is 22?"

There are other attitudes Carnochan wants to change. The VRU, back in its early days, complained about adverts for Irn-Bru featuring a blue cuckoo mimicking a Glasgow hardman.

"Unless we stop glamorising violence and commercialising violence, then we will always have it," he says.

Now, directly on social media, Carnochan takes on those who use violent language, even in jest.

Ahead of this month's general election, former first minister Jack McConnell, who backed the VRU, jokingly tweeted about some girls from his home patch of Wishaw who said they would "effing boot" Tories if they met them.

Carnochan tweeted back: "Why is violence accepted as funny in Scotland?" McConnell said nothing.

The next big change, the ex-cop reckons, has to be in the way men think about women. "How can you protect children if you don't protect their mums? Violence against women is an issue for men, not women.

"It's not enough to say 'I am not a rapist. I don't beat my wife up'.

"The sort of attitudes and behaviour that support that are sexist jokes or the 'beach body ready' stuff."

Carnochan admits he has felt rage. "I have wanted to take somebody by the throat. When I was in the police force we had physical confrontations. We learned to talk our way out of them," he explains "The big thing I have learned? The importance of relationships.

"I remember an academic called Richard Tremblay telling me that we don't learn how to be violent. We learn how not to be violent.

"Babies have temper tantrums. Where do they learn that? They don't see their mums and dads lying on the ground screaming.

"In our early years we learn to negotiate, compromise, we learn empathy."

So what do those who are violent need? "Connections," says Carnochan. "Connections are everything."

Conviction is Book No 9 in the Postcards from Scotland series. £7.99 (inc. p.&p) at www.postcardsfromscotland.co.uk