Paul Stretford, one of the most powerful agents in British football, reacted furiously last night after the FA suspended him for 18 months and fined him £300,000 for improper conduct over his signing of Wayne Rooney. Stretford's anger was shared, if not quite matched, by the Manchester United forward, who is said to be unhappy about the treatment of his agent.

In the culmination of a highly acrimonious three-year case, the FA's independent commission found Stretford guilty of seven charges relating to his acquisition of the rights to represent the 16-year-old Rooney in 2002 and to the evidence the agent provided in a trial at Warrington Crown Court in October 2004, when charges were dropped against three men accused of blackmailing him.

The charges that were proven yesterday included one of “failing to respect the interests” of Rooney and the rights of a third party, Pro-Form Sports Management, which had represented the forward at the start of his career at Everton, as well as failing to lodge representation contracts with the FA and signing the player to an eight-year contract, which exceeded the two-year maximum allowed by Fifa, football's world governing body.

In addition to the fine, Stretford, founder of Proactive Sports Management, has been banned from operating as an agent for 18 months, with half of that sentence suspended. This would mean that Stretford would be excluded from “agent activities”, such as negotiating transfers and contracts, for a stable that includes Rooney, John O'Shea and Nicky Butt.

In theory, Rooney may require another agent - such as Kevin Moran, the former Manchester United defender, who works for Proactive - to negotiate his next contract, but Stretford will continue to represent him until the appeal process has been exhausted. He must pay his fine within 14 days, but, acting on advice from his solicitors, Halliwells, he has outlined his determination to appeal, initially to the FA and then, if necessary, to an independent arbitration body.

“I believe the verdicts of the disciplinary panel against me are a travesty of the facts heard by its members during the hearing,” Stretford said in a statement. “These charges came about as a result of my appearance in a criminal trial as a witness for the prosecution against men accused of blackmailing me with menaces. In pursuing their case against me, the FA seems almost wilfully to have cast me as the accused in the trial rather than a prosecution witness acting properly in the interests of justice.

“It has always been my contention that the FA's case against me should have been heard in public and by an independent panel. Had that been the case, I believe the verdicts would have been very different. I will continue to maintain my innocence of the charges brought against me.”

Rooney, who, along with David Gill, the United chief executive, gave evidence on Stretford's behalf at the hearing, was said to be angry at what he perceives as a campaign against the man who negotiated his first professional contract and his transfer to Old Trafford.

Sources at Proactive suggested that Rooney was “on a collision course” with the FA, which again raises the long-mooted threat of a refusal to cooperate with media or commercial activities while on England duty.

Stretford maintains that Rooney approached Proactive, rather than the other way round, in the summer of 2002 and that a document charting the first agreement between player and agency related to his image rights rather than his representation.

Shares in Formation Group, Proactive's parent company, fell by 1.45p to 16.25p yesterday, wiping £3.3 million off its stock market value, which is now £35.75 million.

Agents in the spotlight

* In recent years, the spotlight has turned on agents' conduct, with close scrutiny of their relationships with clubs and managers, and of their earnings and their influence.

* Last year, the FA charged Luton Town with more than 40 offences: for breaking the rules in the way they paid agents their fees and for dealing with unlicensed agents. The club was fined and docked ten points.

* In 1995, an FA inquiry found that George Graham, then the Arsenal manager, had been illegally paid £425,000 by Rune Hauge, an agent, to sign two players.

* In 2006, after Mike Newell, then the Luton manager, alleged that agents routinely offered “bungs”, the Premier League launched an inquiry into transfers, but struggled to discover any hard evidence. A BBC Panorama investigation claimed that several agents were involved in dubious practices. In the past year, City of London Police made several arrests and searches related to alleged corrupt transfer practices; those involved have denied any wrongdoing.