BBC Panorama has been working with The Times on a joint investigation into the allegations made about Mr Sullivan.
"Over decades, he's made millions from pornography, newspapers, and football. The investigation is due to be broadcast and published on Monday," a BBC spokesperson said.
It is understood none of the claims relate to West Ham or any of its operations, the club said, while Mr Sullivan also added that none concern "my more than 30 years in football".
"I have recently become aware that factually incorrect and entirely false, decades-old allegations concerning my personal life are due to be broadcast and published," he said.
"The false allegations levelled against me have been sensationalised by the media. 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."
Mr Sullivan, who made his fortune from owning pornographic magazines and sex shops, went on to say he will sue "the BBC for libel, along with any other media outlet that repeats any libellous allegations".
"I am a private man, and those who personally and professionally know the real David Sullivan, not the caricature invented by the tabloids, know exactly who I am and what I stand for," he said.
"I am absolutely not the person the media has decided to paint me as."
Until his resignation on Saturday, Mr Sullivan was on West Ham's board of directors alongside joint-chairs Czech billionaire Daniel Kretinsky and Vanessa Gold.
In his statement, Mr Sullivan said his decision to resign came as West Ham faces a "challenging and important time" and he didn't want to create any distractions.
"This has been an incredibly painful decision to make, but it is one made out of love, respect, and responsibility toward a football club and a fan base that deserve absolute unity and focus moving forward," he said.
West Ham were relegated from the Premier League last month after 14 years in the top flight.
The club's demotion to the Championship was confirmed on 24 May despite a 3-0 win over Leeds.
The 2025/26 season saw the club sack Graham Potter as coach in September, after the team lost four out of five games.
Off the pitch, the season has been mired by protest, with fans waving red cards on the 16th minute of the game, to mark the 16 years under Mr Sullivan and Baroness Brady.
In a letter to Sir Keir Starmer, Ms Badenoch said a review was needed to restore the public's confidence and faith in the police following the case, which sparked violence on the streets of Southampton earlier this week.
Mr Nowak, 18, was handcuffed by police after being stabbed, despite telling officers about his injuries.
His murderer, Vickrum Digwa, falsely claimed he had been racist towards him. He was jailed for life on Monday.
The Independent Office for Police Conduct is investigating Hampshire police's response in Mr Nowak's case - but Ms Badenoch argued a government review could provide answers more quickly.
She wrote: "An independent rapid review into the circumstances surrounding Henry's death, including the police response, the subsequent decision-making, and the role of the IOPC would be the best means of ensuring that confidence in policing and the wider system of accountability is maintained.
"It would secure an objective account of events, examine any failings, provide clarity for Henry's family, answer legitimate public concerns, and demonstrate that no institution is beyond scrutiny when public trust is at stake.
"Such a review would be capable of delivering answers within a few months, while remaining independent of Hampshire police and the IOPC itself."
Ms Badenoch added: "Crucially, it would be able to examine the entire chain of events and decision-making, including questions that fall outside the IOPC's own investigation."
Police bodycam footage showed Mr Nowak lying on the ground, handcuffed, pleading for the police to help him after he was stabbed.
Sir Keir has said the footage was "harrowing", adding: "I have to say, as a father of a 17-year-old boy, I felt sick watching it."
Read more:
West Ham joint-chair steps down
Ukraine launches strike on Russia
The case has sparked a political row in Britain and across the Atlantic.
US vice president JD Vance called for "righteous anger" and blamed Mr Nowak's murder on "the mass invasion of migrants".
Mr Vance made the comments on X after the US state department also commented on the case, saying "two-tiered policing" must be rejected in the West.
He claimed Mr Nowak would "still be alive today...if the last few generations of European elites had stood their ground against the politics of self-hatred and the mass invasion of migrants, many of whom despise the West and the people who love it".
"Henry was far from the first to so needlessly lose his life, and I fear he won't be the last," he added.
"Each time a life like his is lost, the proper response - the only response - is righteous anger."
Number 10 hit back, accusing people of "seeking to stir up division on our streets".
The Prime Minister's office added: "The Nowak family are grieving after Henry's horrific murder. They have said they do not want his death to be used to create further division, hatred or tension. We should be respecting their wishes.
"Our politics should bring people together even in the most terrible of circumstances.
"That is who we are as a country."
Senior members of the Royal Family visited the village of Kemble for the nuptials of Princess Anne's son and NHS nurse, Ms Sperling.
Metal barriers were erected and roads closed around All Saints Church, that sits around four miles south of Cirencester, where well-wishers lined the streets to catch a glimpse of the happy couple.
Among the guests included the King and Queen, the Princess Royal, the Prince and Princess of Wales, and the groom's sister and brother-in-law Zara and Mike Tindall with their daughters Mia and Lena, and the Duke and Duchess of Edinburgh with their son James, Earl of Wessex.
Princesses Beatrice and Eugenie also attended, in what is their first public appearance since a new National Audit Office report emerged on the financial arrangements of several members of the Royal Family, including details about how the King has footed the bill for their accommodation.
Their husbands, Jack Brooksbank and Edoardo Mapelli Mozzi, joined them.
The Duke and Duchess of Sussex did not attend.
Members of the public, who had travelled as far afield as Ireland, cheered as Charles and Camilla and William and Kate arrived to see the couple tie the knot.
The well-wishers shouted "hip hip hooray" as the bride appeared with her three bridesmaids - Mr Phillips's children Savannah, 15, and Isla, 14, as well as Ms Sperling's teenage daughter Georgina.
Ms Sperling, who will now be known as Mrs Phillips, wore a dress designed by Emilia Wickstead, earrings by Pragnell and the Pragnell family tiara, with shoes by Jimmy Choo.
Family and close friends headed to Gatcombe Park, the home of the Princess Royal and her husband Vice Admiral Sir Timothy Laurence, for the reception.
However, Charles and Camilla had to make a dash by helicopter to the Epsom Derby, where they were due to present the trophy to the winner.
Read more:
West Ham joint chair step down
Four plead guilty over police clashes
Among the well-wishers were Sarah and Jez Smith, who travelled from their home in nearby Poole Keynes, Gloucestershire.
"It is something that doesn't happen normally on your doorstep," Mrs Smith said.
She also praised the decision to hold the wedding in Kemble.
"It's really important that it is a local church for Harriet."
Peter Phillips is the eldest son of Princess Anne and her first husband, Captain Mark Phillips.
He split from his first wife, Autumn, in 2020 after 12 years of marriage, and began dating Ms Sperling in 2024 before announcing their engagement in August last year.
The couple were guests of the King and Queen at Royal Ascot in June and were invited to take part in the traditional carriage procession to signal the start of the day.
They were among six more people charged after clashes erupted on Tuesday evening between officers and protesters, who were demonstrating against the way police handled the case.
Anger erupted after police body-worn video footage was released following the trial showing 18-year-old student Mr Nowak being handcuffed after his killer Vickrum Digwa, 23, falsely claimed he was racially abused.
Harry Varney, 34, Dillon Crawford, 29, both of Southampton, Taylor Grundy, 22, of Gosport and Andrew Summerhayes, 38, of Romsey, all admitted violent disorder at Southampton Magistrates' Court on Saturday.
Summerhayes also pleaded guilty to two counts of possessing an offensive weapon in public.
Prosecutor Robert Salame told the court Crawford used "large items including bins and chairs" against police officers, while Summerhayes was alleged to have thrown items including bins at police officers.
Mr Salame said Varney refused to move when asked by police officers and pushing against their shields.
The prosecutor said Grundy wheeled a "large, industrial bin" in the direction of police officers.
In a separate hearing, Kevin Reeves, 31, and Andrew Riddett, 38, both of Southampton, did not enter pleas to violent disorder charges.
All six were remanded in custody ahead of their appearance at Southampton Crown Court on Wednesday.
Mr Nowak, from Chafford Hundred, Essex, was stabbed to death on 3 December 2025 while walking home after a night out with friends in Southampton.
Digwa was jailed for life with a minimum term of 21 years on Monday for murdering the university student with a ceremonial knife with an eight-inch (21cm) blade, which he claimed he carried for his Sikh religion.
Digwa falsely told police at the scene he had been racially abused, prompting officers to handcuff the teenager as he lay dying. Police ignored Mr Nowak's pleas that he could not breathe.
On Friday, three people pleaded guilty to violent disorder after the protests in Southampton.
Residents in Russia's second-biggest city were told to stay in their homes after the strike on Saturday.
Regional governor Alexander Drozdenko said 141 drones had been shot down over the surrounding Leningrad region, and Russia's defence ministry said its air defences shot down 376 Ukrainian drones.
No casualties were immediately reported.
Ukrainian President Volodymyr Zelenskyy criticised Vladimir Putin for wanting to "keep fighting" after the Russian president rejected his proposal for a face-to-face meeting on Friday.
"It is time to end this war. But Russia's ruler wants to keep fighting," Mr Zelenskyy wrote on X.
He added: "Last night, our drones covered a distance of about 1,000km (621 miles) to the St Petersburg region - to the enemy navy's arsenals and a base in Kronstadt.
"Our long-range sanctions (strikes) also reached about 500km (310 miles) into the Krasnodar region - and hit an oil depot."
The strikes signify another blow to Mr Putin's efforts to cast the war as a distant conflict that has little impact on daily life.
It followed another Ukrainian drone strike on an oil terminal and naval base near the city on Wednesday, just hours before the St Petersburg International Economic Forum opened.
With the frontline barely moving, both sides have sought to make gains by launching long-range strikes.
A fire broke out at Russia's largest oil-processing plant, the Antipinsky oil refinery, in the Tyumen region, local authorities said via Telegram on Saturday.
Authorities said the blaze was caused by "process violations" at one of the purification units, refuting reports that a Ukrainian drone attack was the cause.
Read more from Sky News:
Technical issue detected on one of UK's biggest warships
WHO announces £386m plan to fight Ebola outbreak
Meanwhile, Russia's defence ministry said on Saturday it had captured the settlement of Shevchenko in Ukraine's Kharkiv region, according to state news agency RIA Novosti.
These reports could not be immediately verified.
In Ukraine, one person was killed and three wounded overnight on Saturday in the Dnipropetrovsk region, as Russian forces struck three districts close to 30 times with drones and artillery, regional head Oleksandr Hanzha said.
In Zaporizhzhia, seven people sought medical care after a Russian drone strike started a fire at a car park, according to regional head Ivan Fedorov.
Russia targeted Ukraine overnight with 272 strike drones, and air defences shot down 249 of them, the Ukrainian air force said on Saturday.
Mr Zelenskyy will meet Sir Keir Starmer, French President Emmanuel Macron and German Chancellor Friedrich Merz in London on Sunday to discuss the war, France's Elysee Palace said.