David Sullivan, the billionaire businessman who resigned as West Ham chairman on Saturday amid allegations of improper conduct, is facing intensifying scrutiny after a joint investigation by the BBC and The Times.

A number of women — all former models who had sought work at the Daily and Sunday Sport newspapers — have made accusations against Sullivan, who built his wealth in the pornography industry. Sullivan has rejected every claim. "The false allegations levelled against me have been sensationalised by the media," he said. "After a lifetime spent building businesses in the adult industry in which I have met thousands of women, it is sadly inevitable that a small number of improper conduct claims are being made against me. I categorically deny these claims."

Regulator steps in

The Independent Football Regulator confirmed it has opened contact with West Ham over the matter and intends to invoke its statutory powers to obtain information from Sullivan.

"These are extremely serious allegations," a spokesperson for the regulator said. "We are in contact with West Ham on this matter and will use our statutory powers to seek urgent information from David Sullivan relating to his suitability under our Owners, Directors and Senior Executives regime. We are unable to comment further at this stage."

Sullivan, who is 77, served on the West Ham board for more than 16 years before his departure on Saturday. His exit comes weeks after the club were relegated from the Premier League.