“It’s like a movie; the windscreen wipers are going and I’m really happy because I’ve got my little baby next to me. I see this man walking down the yellow lines in the centre of the road. He’s all hunched over, soaking wet, and I think, ‘Oh, that poor homeless tramp.’ Then I realise it’s my husband, drunk as a skunk.”

The first face you see in George Best: All By Himself is that of the Manchester United legend’s first wife, Angie, whose voice cracks with emotion as she recalls the moment she knew their tempestuous, but loving eight-year marriage was over.

“I said to myself, ‘I can’t look after both babies… the big one has to go,” she adds.

It’s not the opening Daniel Gordon had envisaged in 2014 when he started making his feature-length documentary, which goes on general release here this fortnight.

“I thought we’d have a more conventional montage of George turning hapless defenders inside out and then some of the warning signs, but that changed during the edit when I listened back to her interview and realised how powerful Angie’s words are.

“The summary tends to be, ‘Footballer, first pop-style superstar, alcoholic’ but George was far, far deeper than that,” he continues. “The key, for me, was putting all the stories you’ve heard about him into their proper context. Instead of having a narrator, we got the various characters, including George himself through old interviews, to tell the story. Somebody said to me, ‘It’s almost like he’s talking from the grave,’ and they’re right.”

Telling contributions are also made by George’s second wife, Alex Pursey, and Jackie Glass, the Swinging London model he dated at the height of his ‘60s Beatlemania-like fame and who’s gone on to become a Buddhist monk. “Jackie’s a very wise lady,” Gordon reflects. “She was going in the same direction as George but managed to pull herself back. When we were doing the interview, she kept saying, ‘I don’t want to be preachy, I’m not making a judgment on him or anything.’ I thought she was incredible.”

It’s not all gloom, doom and squandered talent, though, with the Mancunian doing a brilliant job of showing how George went from kicking a ball round on East Belfast’s tough Cregagh estate to lifting the European Cup in five insanely action-packed years.

“The goal he scored against Benfica in that final was the pinnacle of his career. That amazing image of him with his arms raised and the number 7 on his back… it never gets better than that. There’s a great Harry Enfield moment during the Northern Ireland vs. Scotland game when the commentator goes, ‘The ball is tied to his feet…’ He produced these amazing bits of skill even when the pitches were mud baths and he had Chopper Harris hacking him to pieces. You’re watching those skinny little legs and he’s got no shin pads on. Because his dad, Ted, is a massive fan, David Beckham grew up thinking that George Best was the greatest thing that ever lived.”

Asked whether he thinks George is the finest player this island has ever produced, Gordon immediately shoots back: “By a long shot. I have absolute love and respect for Paul McGrath and Liam Brady, but they couldn’t have scored that goal against Fulham, or the one we have in the film from his San Jose Earthquakes days when George slaloms his way through the entire Fort Lauderdale Strikers defence. He beats the same guy three times before sticking it into the net!”

George’s ability to recognise that he was comprehensively screwing up – “I’m my own worst enemy,” he admits in an early ‘70s interview – but then seriously repeat his mistakes reminds me of Amy Winehouse.

“We were half-way through film when Amy came out and, yeah, I did think there were similarities between her and George when I went to see it. There was awareness to a point, but neither was able to act on it. I felt a bit envious watching Amy, too, because there were no handicams back in George’s day. The Bests were a working-class family from Belfast, so they weren’t Instagram-ing themselves everyday or whatever the ‘60s equivalent was! Tracking down footage was hugely difficult, but we found some great stuff like the ad he did for Cookstown, ‘the Best family sausages’!” Few Northern Irish public figures have managed to straddle the sectarian divide with the ease George Best did.

“Growing up I didn’t know which community he was from because he never discussed politics. He got threats from the IRA, but chose not to make a big deal of it. Two hundred and fifty thousand people were at his state funeral, which speaks volumes. I was very struck by the love there is for George in Belfast still.”

Angie Best’s view is that he made a decision every day to drink whereas her sister, who also knew him well, would be of the opinion that it was a disease he couldn’t control.

“My dad, who’s worked in alcohol addiction, says there’s no empiric evidence either way. There are arguments for both, I think. The odd thing is that George drunk the heaviest when things were going well for him. It was almost a deliberate, ‘Okay, I’m going to fuck this up.’

“George’s get out of jail card was that he was very handsome and charming and – for a while at least – only had to flash that smile to get forgiveness,” Daniel continues. “George had that charm, the twinkle in the eye. He kept on being given second, third and fourth chances, which meant that he didn’t really have to modify his behaviour.”

In stark contrast to George, the Belfast lad who went over with him to Old Trafford, Eric McMordie, remains impossibly fresh-faced.

“You can’t help looking at Eric and thinking, ‘If only George had taken care of himself like that…’” Gordon nods sadly.

Insights into what it was like to kit-up alongside Bestie are provided by that fellow member of Man U royalty, Paddy Crerand.

“Paddy also made his United first-team debut in 1963, but had five-years experience playing for Celtic and was a big brother figure to George. He saw what was happening to him but couldn’t do anything about it, which I think haunts him a bit. More so than even now it was considered ‘a man’s game.’ There was nobody you could go and talk to about your mental health issues. In those days if you were down, you just went out with your mates, got drunk and slept it off the next morning. You have to remember that it was totally unchartered territory for a footballer to have 30 reporters camped outside his door, and to be the subject of a nationwide manhunt when he went missing for a few days.

“There’s footage in the film where he’s basically pleading for help. He’s got depression and needs professional care, but they had absolutely no idea in 1972 how to deal with it.”

Wasn’t United manager, Sir Matt Busby, supposed to be his father confessor?

“Yeah, but he’d never comes across anything like that before,” Gordon reasons. “He tried bollocking him out of it; that didn’t work. He fined him two weeks wages. That didn’t work either. He banned him for a while; same non-result. We got some low-resolution film of George finally quitting and leaving Old Trafford for the last time in ’74. It was only when we got it transferred and cleaned up that you could see there were tears in Matt Busby’s eyes. It was just, ‘Oh my God, the level of that relationship.’ Even though he let a lot of them down, people loved George.”

George Best: All By Himself screens in the IFI, Dublin and other select Irish cinemas from February 24.