Alex Ferguson will today find himself facing the ordeal of a second legal dispute with John Magnier and JP McManus when Manchester United's rebel shareholders inform the club they are investigating a possible claim for defamation.

aIn their most aggressive move to date, legal representatives of Magnier and McManus are writing to Manchester United's board to demand the tapes and written transcripts of Ferguson's various interviews with newspaper, television and radio journalists at the club's training ground in Carrington last Friday.

It follows Ferguson's disclosure - repeated almost verbatim in every interview - that his son Jason had called in the police at the end of a "distressing" period in which "people have been stealing his mail and his bin-bags and hiding in bushes outside his house". Magnier and McManus feel he could have been unjustly referring to them.

Ferguson, who is suing Magnier over the disputed rights to stud fees for the former racehorse Rock Of Gibraltar, now faces the possibility of his highly influential detractors lodging a high court claim for defamation.

From their winter retreat in the Caribbean Magnier and McManus, who have admitted hiring private investigators to examine business activities at Old Trafford, have instructed solicitors working on behalf of their company Cubic Expression - majority shareholders in United with a 25.49 per cent stake - to investigate whether there are grounds to make an official complaint. Their legal team has collected a dossier of newspaper cuttings and may request recordings from Sky, the BBC and the club's own channel MUTV.

The threat of legal action will be made clear in a strongly worded letter marked for the attention of United's plc chairman Roy Gardner and the club's chief executive David Gill.

Maurice Watkins, the non-executive director who doubles as the club's solicitor, will almost certainly have to get involved and the board of directors will need to ascertain from Ferguson exactly what he meant before drafting a response.

Whether they can stave off another potentially damaging legal case may depend largely on what Ferguson has to say, but about the only certainty now is that the latest development in an increasingly acrimonious case will dismay senior figures within Old Trafford. The club's hierarchy had been hoping Ferguson and Magnier were moving closer to an out-of-court settlement but events since the weekend have made it clear that, if anything, the two sides are more bitterly divided than ever.

By threatening a writ of their own, Magnier and McManus seem to be continuing a strategy aimed at undermining Ferguson.

The Irishmen are entitled to believe they have moved into a position of strength. In particular, they know they are making life difficult for the 62-year-old at a time when he is under intense pressure to either withdraw his claim for joint ownership of Rock Of Gibraltar's breeding rights or open talks for an out-of-court settlement that would see him drastically reduce his demands.

Last night Ferguson's legal team provided written documentation to Magnier detailing the reasons behind his claim, as demanded by the High Court in Dublin.

Sources from Magnier's camp have suggested the racing tycoon is hardening his position regarding Ferguson's action and the only deal he will accept is the one he initially offered - a single cover each year for the remainder of Rock Of Gibraltar's life - which the long-serving United manager has already flatly rejected.

Magnier twice granted extensions to the timeframe Ferguson's legal advisors had to provide the answers and no doubt the Irishman's own lawyers will be poring over the details trying to establish on exactly what basis the Scot is taking his action.

Tomorrow, when the letter from Cubic Expression lands on their desks, Gardner and Gill hope to be in a position to send their official response to the earlier correspondence from Magnier and McManus in which they raised 99 questions about transfer dealings and other business activities at the club. As yet, the details have not been made public. Chief executive David Gill has already announced that finance director Nick Humby will lead a "thorough internal review" of the club's structures, although this news was met with a stony response from the Irish camp, who had asked for an independent audit.

Extra security was in evidence at Taunton racecourse yesterday stemming from fears that Manchester United supporters might try to interfere with two horses owned by McManus which were running there. No trouble materialised and neither of McManus's horses finished its race.