And even fewer have enraged the Scot like 68-year-old football agent Mel Stein did in 1988 when his most famous client, Paul Gascoigne, chose to sign for Tottenham Hotspur instead of United.

"He absolutely blames me for Gazza not signing for United," Mel told me at the Four Four Jew exhibition at the Jewish Museum London.

"I was informed by someone trustworthy that he later said that if he saw me walking on the street, he would hit the accelerator rather than the brake."

Mel - the working class London boy who grew up to represent some of the biggest names in football - is now the co-founder, alongside Jon Smith, of the Association of Football Agents.

So perhaps he is in a position to properly evaluate how 'dirty', if at all, the football agency world is.

"It is much cleaner than it was when I first started out 35-years-ago," he said. "If you examine the facts, there was probably only me and four or five others who were really working hard at it. But now, wow.

"There are more than 500 and it has become a rat race, but that has helped clean football up because each agent has to be totally above board.

"If they aren't, then a player will find another agent to represent them."

Mel was born in North London and raised on a council estate.

The son of a barber, he grew up without luxuries.

He was educated at the Central Foundation Grammar School and King's College London and was recognised as one of the first solicitors to be regarded as a specialist sports lawyer - now a boom industry.

Away from the cut-throat world of football, Mel also established the post graduate certificate in Sports Law at King's College in 1995 and still lectures on the topic.

Former footballers such as Chris Waddle and Alan Shearer, as well as several Football League clubs have sought representation and legal advice from Mel over the years, but they pale in comparison next to Paul Gascoigne, the erratic midfield who he is best known for advising.

"Gazza was like a third son to me," he insisted. "We had some incredibly good times together and I still love him.

"He struggled with addictions that he simply could not control in his own head.

"If you look back now, the success we had together was mindblowing, especially around the World Cup in 1990.

"The only player I have seen since that even came close to matching that level of hype and celebrity is David Beckham.

"The merchandising and sponsors were so unique at the time, but in the end everyone wanted a piece of him.

"What Gazza needed more than anything was to grow up a little bit.

"But everything came so quickly for him and he never had much of a childhood, so he never grew up and never got the fun out of his system."

One story that Mel has often retold over the years involves Gascoigne displaying his rear end against a window while he was signing his contact with Italian giants Lazio, all so the gathering crowds outside could have a bit of fun.

"To the casual observer that was funny," Mel explained. "But not to the people who cared about him. He was 25 and needed desperately to get a grip and realise that the people around him in that room were not fans, but serious businessmen throwing a lot of money at the deal."

Mel, who trained as a solicitor in commercial law, grew up a Newcastle United fan and turned his back on the 'family team' Arsenal - his decision was made when Newcastle defeated the Gunners in the 1952 FA Cup final.

"Because I was a Newcastle fan, I got to know a few people at the club," he recalled. "I was eventually introduced to Chris Waddle and acted as his lawyer.

"Over time I became his agent and he led me to Gazza.

"I think it's important that football agents coming into the game now have an academic background because you need smarts to make it in this game.

"That is what I tell all the young people who call me for advice.

"I get loads calling, asking what the secret is. Some are dedicated, hard-working and willing to learn, but others are looking for a quick fix.

"I tell them that there is no such thing, that everything you want needs to be earned.

"I absolutely did that and worked hard for all that I have.

"And then once you are an agent, you need to be shrewd, smart and honest as well as have a deep understanding of the way sport works."

Mel has plenty of interests away from the game and is the author of 18 books, including How to be a Sports Agent and a biography of Gascoigne.

Mel's son Paul is director of fundraising and marketing communications at World Jewish Relief, an organisation Mel supports.

One of the issues that riles supporters is the salaries earned by players, but Mel, like many in the sport, states that players are paid what the market dictates.

"One thing I can guarantee is that the clubs make more than anyone," he insisted.

"It's all about market forces and getting the best deal possible for your player.

"But don't expect much loyalty back, I did some great deals for players who then betray you. Players can be a fickle bunch."

While players might be fickle, Mel insisted that one man is not and he laughed off the notion shared by Sir Alex Ferguson that he "never held a grudge".

Rather emphatically Mel responded: "He did with me."