A 29-year-old man has been arrested on suspicion of fraud after allegations that Tottenham Hotspur FC spied on Olympics officials during its stadium bid.
News of the arrest came as Olympic Park Legacy Company (OPLC) chairwoman Baroness Ford claimed the north London football club had all 14 members of her board monitored by private investigators.
The suspect was being questioned as officers conducted a string of searches in Sussex, Sutton, south west London, and Westminster.
Spurs denied putting officials under surveillance.
Detectives, who have been investigating the claims since August 2011 "following allegations by West Ham and the Olympic Park Legacy Company in respect of the unlawful obtaining of information", said the suspect was arrested at an address in Sussex.
He was taken into custody at a Sussex police station "where he remains", said a spokesman.
"As part of their inquiries, detectives have conducted searches at both a residential and business premises in Sussex, a second private address in Sutton, and a further business address in Westminster," police said.
Baroness Ford, chairman of the OPLC, which is in charge of securing a viable economic future for the home of the London 2012 Games, told the London Assembly earlier: "My board were put under surveillance by Tottenham Hotspur and the chairman of Tottenham Hotspur felt confident enough to say in the Sunday Times several months ago that all 14 members of my board were put under surveillance. The Metropolitan police are now conducting an investigation into that surveillance.
"There has been all kinds of behaviour here that I could not have anticipated which, believe me, has not been pleasant in the last 12 months."
Tottenham Hotspur Football Club rejected Baroness Ford's comments and issued a statement through its lawyers, which read: "The club did not undertake, instruct or engage any party to conduct surveillance on any member of the OPLC Committee and we consider the making of this baseless accusation to be wholly inappropriate and irresponsible. We totally reject the accusation in the strongest possible terms."