The wealthy co-owner of a Premier League football club made a £1m loan to a company controlled by David Hunt – three months after a High Court judge named Mr Hunt as the head of an organised crime network.

A company owned by David Sullivan, the multi-millionaire boss of West Ham United, lent the money to the East End businessman's property company soon after Mr Justice Simon concluded that Mr Hunt led a gang involved in fraud, money-laundering and "extreme violence".

The loan was secured against several of Mr Hunt's properties, including a golf club in Essex and a restaurant once owned by the actor Sir Sean Connery and the late West Ham captain Bobby Moore, who led England to World Cup glory in 1966.

Mr Sullivan's company, GC CO NO 102 Limited, made the loan to Mr Hunt's company in October last year. In January, Mr Sullivan, a former pornography tycoon listed as Britain's 224th richest man with assets worth £400m, placed this company into voluntary liquidation and declared liabilities of just £90, suggesting the loan to Mr Hunt had been quickly repaid.

David Hunt – nicknamed "Long Fella" – was officially exposed last summer in a judgment by Mr Justice Simon after the crime boss brought an unsuccessful libel action against The Sunday Times.

A catalogue of damning claims emerged during the trial, including allegations that Scotland Yard viewed Mr Hunt's gang, which had operated with impunity for more than 20 years, as "too big" and "too dangerous" to take on. During a covert operation codenamed Blackjack, the Metropolitan Police placed bugging equipment in a car showroom, which picked up an attack by Mr Hunt in which he had slashed the face of a man named Paul Cavanagh, who had upset an associate.

Mr Hunt was arrested and charged with the attack. But the prosecution dropped the case after Mr Cavanagh withdrew his statement to police. A High Court judge would later find that Mr Hunt had intimidated him into not giving evidence for the prosecution. Mr Justice Simon also concluded that Mr Hunt had attacked and threatened to kill Billy Allen, a property developer, in 2006. "It was the sort of power and authority that might be expected from the head of a criminal network," said the judge, who also ruled that Mr Hunt had engaged in money-laundering.

Three months after the libel trial had concluded, Mr Sullivan's finance company made the £1m loan to Mr Hunt's company, Hunt's UK Properties. The West Ham co-chairman's loan was secured against several properties including Woolston Manor Golf Club in Chigwell, Essex. This luxurious setting has twice come to the attention of investigators in unconnected matters. In 2006, Metropolitan Police officers raided the club and found cases of Bollinger champagne which had recently been stolen from a lorry. In 2008, Peter Pomfrett, a director at the same club, was jailed for 10 years over his role in a £37.5m fraud.

Two months after Mr Sullivan's company made the loan to Mr Hunt's firm, our sister newspaper The Independent revealed a secret Metropolitan Police report – codenamed Operation Tiberius and dated 2002 – which concluded the crime-lord's gang had been helped to evade justice by a network of corrupt serving and former police officers.

"The Hunt syndicate has developed an extensive criminal empire which has so far evaded significant penetration from law enforcement," said the Operation Tiberius report. "The syndicate has achieved this invulnerability through a mixture of utilising corrupt police contacts and the intimidation of witnesses brave enough to give evidence against them." It added: "The Hunt syndicate is one of the most violent groups in north-east London and has been responsible for a series of vicious assaults against debtors and rivals. Their main sphere of influence is drug importation and protection."

The report by the Met's anti-corruption team names four Met detectives "associated" with the syndicate, one of whom is high-profile and has given evidence to Parliament. Operation Tiberius reported that corrupt officers betrayed the Met by telling the Hunt syndicate about tracking devices placed on its vehicles, leaking information about police inquiries and carrying out checks on police intelligence databases. Scotland Yard refuses to comment on Operation Tiberius.

In the same month that The Independent reported details of Operation Tiberius, Mr Sullivan placed GC CO NO 102 Limited into voluntary liquidation.

The 65-year-old made his fortune in pornography magazines and sex shops during the 1970s. In 1986, he founded the Sunday Sport newspaper, offering fanciful stories with headlines such as "World War 2 Bomber Found on Moon". Mr Sullivan moved into sport with the acquisition of Birmingham Football Club in 1993, appointing Karren Brady – star of The Apprentice, who is close to David Cameron and George Osborne – as managing director. He sold up in 2007 and bought West Ham in 2010.

Mr Sullivan's club has secured Premier League survival this season under manager Sam Allardyce. In two years' time, West Ham will move into the Olympic stadium in Stratford, east London, which was built for the 2012 Olympic Games using £500m of taxpayers' money.

A spokesman for Mr Sullivan said: "GC CO NO 102 Limited is a finance company, it makes loans to numerous people and companies. This was a normal commercial loan at a normal commercial rate."