Alex Ferguson's complaints that he has been under attack from the media all season could increase tomorrow night when BBC shows the Ferguson Factor, a biography of the Manchester United manager.

After being accused of trying to persuade young players to sign for his agent son Jason and ridiculed last week for an expletive-ridden defence of Juan Sebastian Veron, Ferguson is likely to be further enraged by the documentary.

In fact the programme, which airs a foul-mouthed tirade at John Motson and in which Eric Cantona accuses United of treating him like "a shit", is the subject of a letter from Ferguson's lawyers to the BBC.

Undoubtedly the most shocking moment is the 1995 incident with Motson.

Until now, claims the programme's narrator Michael Crick, who also wrote the biography detailing Ferguson's use of his son as an agent, Match of the Day has been too scared of reprisals to show the footage.

Roy Keane had just been sent off for the third time in 14 matches. Motson asks: "I appreciate that you keep your disciplinary action inside the club, but is the Roy Keane situation one you will have to address?" Ferguson replies: "John, you have no right to ask that question. You are out of order.

"You know fine well my ruling on that, right? That's the interview finished." Ferguson then addresses Motson in increasing fury. "I'm no' wanting that on," he says. "I want to cancel that interview right? The whole fucking lot of it. Cancel it.

"You know the fucking score, son, so fucking make sure that it doesn't go out or you'll never get in this fucking club again. You're fucking not getting in again."

Motson: "Well I was asked to ask you, Alex." Ferguson: "You fucking know the rules here."

The timing is unfortunate for Ferguson, who indulged in a similarly abusive session with journalists when the subject of Veron came up. On Saturday evening Ferguson claimed that he was the subject of "personal" attacks.

The programme recounts a 1978 industrial tribunal that unanimously supported St Mirren's right to sack him for "the arrogant, overbearing way he tried to run the whole club" and that stated that Ferguson had "neither by experience nor talent any managerial ability at all".

The programme extends the claims in Crick's biography that Ferguson unfairly favours his son's agency in its reference to Jaap Stam's sale this season. "Jason's firm is said to have charged Lazio more than £1 milion for a deal which was clearly rushed," it claims. "If they had let other clubs bid, United might have made more money." At least as distressing for the more sentimental United fans will be the sight of Cantona sharing his feelings about why he retired in 1997.

Having scored the FA Cup-winning goal in 1996 to win the Double, Cantona quit a year later. "I signed a contract and they didn't respect anything," he says. "So, at this time I thought that merchandising was more important than the team and the players.

"When the business is more important than the football, I don't care, I just give up.

"But I'm treated like a pair of socks, like a shit. I'm not a shit."

Guardian service