The former adult entertainment magnate David Sullivan has resigned immediately as joint-chair and director of West Ham. In a statement released on Saturday, Sullivan and his lawyers explained that the 77-year-old is stepping down to focus entirely on refuting what he calls unfounded claims about his private behavior.

The Guardian has learned that BBC Panorama has contacted Sullivan regarding an upcoming episode scheduled to air in the next few days.

Sullivan, who built his wealth in the adult industry before launching the Sport newspapers, stated he is resigning to ensure full transparency.

He offered no further details on the claims but rejected them outright as factually wrong and completely untrue. Sullivan warned he would pursue legal action against the BBC should the allegations be aired.

After decades in the adult sector where he encountered thousands of women, Sullivan noted it is sadly inevitable that a small number of misconduct claims would surface.

He portrayed himself as a private individual rather than the exaggerated figure created by tabloid coverage.

Sullivan insisted he is not the person the media has portrayed and questioned the verification process behind the claims. He described the approach as unfair and lacking impartiality.

He confirmed plans to sue the BBC for libel along with any outlet repeating the claims.

None of the allegations involve his three decades in football, he stressed, adding that West Ham has been a major passion. Sullivan said he refuses to let personal issues distract the club during a difficult period and therefore resigned as joint-chair and director immediately.

He is stepping down to devote full attention to fighting the claims and has instructed lawyers to begin proceedings seeking full redress.

West Ham supporters have grown frustrated with Sullivan in recent seasons. Tensions peaked last month after the team finished 18th and dropped out of the Premier League. Sullivan faced jeers during the final match against Leeds United and departed early.

Behind the scenes the atmosphere has been described as chaotic for weeks amid the looming relegation. Several senior figures have departed, including vice-chair Karren Brady who left in April.

Some board members had reportedly sought to remove the unpopular Sullivan, who acquired a 50 percent stake in 2010 alongside his late partner David Gold after they owned Birmingham City.

Sullivan remains the largest shareholder and club sources indicate the club now faces uncertainty over its finances following relegation to the Championship.

Engaged to reality star Ampika Pickston, Sullivan reportedly informed friends on Friday of his intention to resign before lawyers prepared the statement.

In closing he thanked everyone connected with West Ham for their loyalty and memories and expressed confidence in the remaining board and interim CEO Karim Virani.

He will make no further public comment but reserves all legal rights regarding any false allegations.

A West Ham spokesperson confirmed Sullivan resigned as a director of both the holding company and the club after learning of impending serious historic allegations unrelated to the club. Sullivan denies any illegal conduct and stepped down to prevent disruption while addressing the matters privately.

The BBC has been approached for comment.