A 29-year-old man was arrested on suspicion of fraud today after allegations that Tottenham Hotspur 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 this afternoon 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", a spokesman said.
"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.
"An amount of material was seized during the searches."
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: "The thing that I have learned in the last 12 months is that there has been all kinds of behaviour. There has been legal challenges and people have stood behind it anonymously - all kinds of things have happened.
"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 rejected Baroness Ford's comments and issued a statement through their 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."
A deal with West Ham and Newham Council to use the stadium in Stratford, east London, after the 2012 Games, collapsed last month amid legal challenges, with the Government announcing that the stadium would remain in public ownership.
Tottenham had already lost out to West Ham in the race to become the OPLC's first choice to move into the stadium after the Games.
Challenges by Tottenham Hotspur and Leyton Orient, plus an anonymous complaint to the European Commission, had led to fears that court action could drag on for years while the stadium remained empty.
A new tender process is being launched by the OPLC and the showpiece venue, complete with an athletics track, will now remain in public ownership and be rented out to an anchor tenant.
Baroness Ford told the London Assembly's Economy, Culture and Sport (ECS) Committee: "I am expecting the unexpected because that is what the last 12 months has taught me.
"Our job now is to narrow as far as we possibly can the scope now for legitimate legal challenge in this next process - that is all that we can do.
"If people want then to be vexatious, frivolous and vindictive or whatever they want - they will do that."
ECS committee chairman Dee Doocey said: "I personally find it appalling, and I am sure I speak for the rest of the committee, at the very idea of your board being put under surveillance is reprehensible.
"It almost beggars belief that this thing can happen. The idea that any board can be put under surveillance is absolutely disgraceful."
Scotland Yard's Economic and Specialist Crime Command is leading the investigation.