Three men, including an investigator who worked for a company hired by Tottenham Hotspur during a bitterly contested battle for tenancy of the Olympic Stadium, have pleaded guilty to unlawfully obtaining the phone records and bank statements of West Ham vice-chair Karren Brady and others.

Howard Hill, who resigned as a partner from accountancy firm PKF in December 2011 and was arrested in January 2012, pleaded guilty at Inner London crown court to unlawfully obtaining personal data such as phone bills and bank records from executives working for West Ham and the Olympic Park Legacy Company.

The 59-year-old from Stockport was working as a senior investigator for PKF when it was hired by Tottenham Hotspur to perform "due diligence" at the climax of their ultimately failed battle to win the tenancy of the Olympic Stadium in March 2011.

The battle between Spurs and their Premier League rivals West Ham was marked by allegations of dirty tricks, before West Ham was finally awarded the stadium only to see the deal collapse amid "legal paralysis" and court challenges.

Two other men – Richard Forrest, 31, and Lee Stewart, 40 – also pleaded guilty to the same offence and all three will be sentenced on 20 December. Three counts of fraud by false representation were left to lie on file.

Spurs have repeatedly insisted that they knew nothing of Hill's illegal behaviour and PKF, which has since merged with BDO, has also said it was unaware of any illegal activity.

It emerged in a civil suit launched by Brady and West Ham in November 2011 that illegally obtained copies of her phone records had been obtained by PKF during the course of its investigation.

They were alleged to have formed the basis of a story that appeared in the Sunday Times in June 2011 that made a series of allegations about West Ham's behaviour during the bidding process, including the claim that an OPLC director had been paid by the club for consultancy work.

Officers from the Metropolitan police's special enquiry team launched Operation Polworth in August 2011 following allegations by West Ham and the OPLC relating to the unlawful obtaining of information.

A total of six people were arrested through the course of the investigation. The remaining three individuals were subsequently released with no further action.

Detective Superintendent Nick Downing, from the specialist, organised and economic crime command, said: "The special enquiry team conducted a thorough investigation in this complex case and we are pleased with the guilty pleas. The unlawful accessing of individuals' personal data by any means is totally unacceptable."

The tender process for the stadium was eventually restarted by the legacy unit, by then renamed the London Legacy Development Corporation, and a new deal agreed with West Ham in March 2013 to move into the £429m stadium in 2016 following a £160m conversion project.

During the civil case to obtain the records, Brady's case notes revealed that an individual calling themselves "Thomas Brady" with a fictional West Ham email address had managed to obtain the east London club vice-chair's itemised Vodafone mobile phone bills.

Ben Jaffey, the counsel for Brady, said then that PKF claimed not to know where the documents had come from and said that Hill had claimed the telephone records arrived "in the proverbial brown envelope".

The saga of the fate of the Olympic Stadium has proved a long running headache for the government and London mayor Boris Johnson, but both claim that the ultimate solution of a 55,000-capacity multi-use stadium that will host football in the winter and athletics in the summer is the best outcome.

The stadium will be fitted with a full roof and retractable seats that will move over the athletics track, and is scheduled to host matches during the 2015 Rugby World Cup as well as the 2017 World Athletics Championships.