“It was like a strange dream,” Joe Johnson says as he remembers becoming the world snooker champion 40 years ago as a 150-1 outsider and former gas board and factory worker who was the father of six children. Johnson had never previously won a game at the Crucible and he had struggled for years to make a living as a pro.

It was a time when Britain was “snooker loopy” and Johnson played characters such as Bill Werbeniuk who, in 1985, beat him in the first round while drinking a staggering amount of beer.

The following year, Johnson outplayed the great Steve Davis in the world championship final. He was suddenly outrageously famous and became the lead singer for an obscure band, Made In Japan, who then had a hit record.

Johnson reached the final again the following year – with Davis avenging the 1986 defeat – but never won another ranking tournament. Hard times followed as he had to sell the large house he had bought after winning the worlds. Johnson survived seven heart attacks as his fading career was given a sobering perspective.

On a quiet morning in Chiswick, where Johnson is working as a commentator on the current world championships for TNT Sports, the amiable 73-year-old relives everything. In a rare but moving reflection, he also discusses his mixed race heritage and how he endured racism while growing up in Bradford. But there is no bitterness in Johnson as words tumble from him.

“I was thinking: ‘Is it really me?’” Johnson says, recalling how he felt after his brilliant attacking snooker won the world title. “I couldn’t get my breath because I expected Steve to beat me. He was a different player to the Steve I had always beaten as an amateur. He had already been world champion three times. So when I beat him, and won £70,000, which was a huge amount of money then, it really was a beautiful dream.”

Johnson also describes “a very dark time when I was signing on in 1982”. He had turned pro in 1979, when he was already 27, having reached the World Amateur Championship final a year earlier. But he began to “doubt my ability when I didn’t do well straight away as a professional. I was facing experienced pros who knew how to stop an up-and-coming kid.”

The real challenge was that, “when I started, there were only two professional events – the worlds and UK championship. If you lost early there was nothing to feed a family.”

As more tournaments emerged, Johnson’s fortunes improved. But he had a poor record at the worlds. In 1984, on his Crucible debut, he was crushed 10-1 by Dennis Taylor in the first round: “My mum had a heart attack on the Friday and I played Dennis on the Saturday. It was horrendous.

“The next year I played Bill Werbeniuk in the first round. Bill hadn’t won a match all year and I beat him comfortably every time in exhibitions before the tournament. Then, in Sheffield, he was a different man [Werbeniuk raced into a 4-1 lead].

“It was a confidence-builder for Bill and of course he drank a lot. He had six pints before we started and then a pint during every frame. So he had 18 [Werbeniuk won 10-8], plus the six and four pints in the interval.”

I remember watching Werbeniuk, and being stunned by his prodigious drinking while playing, but 28 pints? “It’s true. I’m not exaggerating. I played Bill for money in Australia in 1978 at a billiard hall and he carried a crate of booze up the stairs. I said: ‘Are you drinking them while we’re playing?’ He said: ‘I’m going to drink them before we play.’ He drank a full crate of beer before the match and, again, beat me.”

In 1986, Johnson finally broke his Crucible hoodoo and won two matches before facing his friend Terry Griffiths in the quarter-finals. “Terry always seemed to have my number and I’d never beaten him. I decided to play him differently and go for everything. It worked because I was 9-7 up going into the last session, but all of a sudden he played really well. He won five on the trot to go 12-9 up and it was first to 13.

“It relaxed me because in my mind I was going home – so go out attacking. It worked as I made it 12-12. In the final frame he played a safety shot, which left a really difficult red. Normally, I would have played a safety, but I went for it and got it. I then knocked in a red and it’s probably one of the best shots that anybody’s ever played, not just me.”

Johnson had been in pain, because of a cyst on his lower back, throughout that match. He was in agony in the semi-final and locked at 8-8 against Tony Knowles told the tournament director he was retiring. “But a doctor came over and burst the cyst. It gave me such relief and I won the next eight frames to win 16-8.

“It meant I didn’t need any painkillers before the final. They were horrible because they subdued me – without them my mind was clear and I played my natural game.”

Before the final he and his wife, Terryl, “went shopping in Sheffield and she saw these pink, red and white shoes. She said: ‘They’re gorgeous. Buy them, Joe.’ When I said yes she told me I had to wear them in the final. She talked me into it and during the match I was slipping all over the place. So she took them outside and rubbed them on the pavement and that helped.”

Johnson had few other worries facing the usually remorseless Davis. “Steve didn’t hold any fears for me because I’d beaten him quite heavily as an amateur. I was totally relaxed. If you watch it back you can see I’m joking with the crowd. It was 8-8 after the first day and I then had two really good sessions to win [18-12]. I really enjoyed it.”

His fame was sealed: “The 1985 final [which Taylor won 18-17 on a black ball finish after midnight against Davis] is credited with the most viewers for a snooker match at 18-and-a-half million. Mine was 18 million. But a BBC guy said mine was by far the most viewed because we finished at half-nine when every pub in England was crammed with people watching the snooker. There were only four channels so people were glued. He said my viewing figures were something like 40 million. But becoming so famous was very difficult because snooker was absolutely mega. Me and my wife couldn’t go anywhere. Not even Tesco.”

Was there anything he liked about being famous? “I liked it because famous people liked me. At some function Princess Diana was shaking people’s hands, moving down the line, but when she came to me she stopped: ‘Oh, you’re the snooker player with the pink shoes.’ After talking a while she said: ‘Do you like tennis?’ I said: ‘I love tennis.’ She said: ‘Would you and your wife like to go?’ When I said yes, Diana asked: ‘Is there a star you would like to go with us?’ I chose Cliff Richard.

“So the four of us went to the tennis. My wife wanted to sit next to Diana and I wanted to sit next to Cliff, but it didn’t work out. When we sat down, Terryl whispers: ‘Cliff’s sat on my dress. Would you ask Diana to swap?’ I said: ‘I’m not asking her that. It’s disrespectful.’ So Cliff sat on her dress the whole time. She wasn’t happy.”

Did Cliff at least live up to Johnson’s expectations? “Oh, yes. I was in awe of him, but he was lovely. I met him again after I went to his show and he told the audience: ‘Joe’s here.’ I was so well known he didn’t have to say Joe Johnson. He said: ‘I’d like to invite him backstage for a cup of tea.’ I was embarrassed, but I went and the two of us ended up singing together in his dressing room. It was magical.”

Problems in his career soon emerged. “My eyesight went in 1988 and I struggled on for another four years. But once I slipped out of the top 16 the big money events disappeared. One of the most disappointing things was having to sell the house because I couldn’t afford the repayments. That was 1991-92. I also had my first heart attack in 1991.”

Did Johnson think he was dying? “I did. I was in the gym and couldn’t get up. The manager phoned an ambulance and they carried me out.

“I had seven heart attacks, but then I had a quadruple bypass and the surgeon said: ‘If you don’t stop smoking it’s over.’ I’ve been OK since then.”

It was a humble ankle injury, Johnson says, that ruined him. “If that happened now I’d drop off the tour and then, when my ankle’s mended, go back at the same ranking. But my ranking fell and I was knocked off the tour. They changed the rules after that but it was too late for me.”

I surprise Johnson when I ask about the fact he was born Joseph Malik. His father was from Pakistan and Johnson says: “I lived with him till I was 12 and then, through various reasons, my mother got custody and my stepdad adopted me when I was 13.”

Does he still feel part Pakistani? “Of course,” he says softly. “I’m mixed race and I was one of the first. When I went to school there was only me.”

Was Bradford difficult for him growing up? “It was. Especially in infant and junior school, and then in seniors as well. It toughened me up, without a doubt. It was lonely in a way. There were very few friends, although the friends I did have, both English and Pakistani, were very good.”

Has he ever visited Pakistan? “No, but I do communicate with my family in Pakistan. I’d like to go, but just never had the time.”

Did he endure racism in snooker? “No. It was the opposite because I was so good. People respected my play. Since being a snooker player, from about 15, I got respect. People treat me as a person rather than a colour.”

We chat for another hour and I eventually ask Johnson if he gets tired of talking about 1986? He smiles. “Well, somebody mentions it every week. Not as much as before, but I still get recognised. I realise how fortunate I was to be world champion. I think of sliding doors because Griffiths led 12-9 and he’s got a straight green into the green pocket. He hadn’t missed anything. But he missed that green. From that moment, I didn’t miss.

“If he pots the green I’d never be world champion. I wouldn’t have had all these exhibitions I’m still doing. I wouldn’t be commentating now. My whole life changes on one missed shot. I feel lucky because of that. I’m delighted and so I’ll never get tired talking about 40 years ago.”