MORE than 20 people have been questioned by anti-corruption investigators probing allegations of collusion during a government land auction in which a ''cartel'' of developers combined to suppress property prices. The Independent Commission Against Corruption (ICAC) confirmed yesterday that an official inquiry had started after the lodging of several complaints. ICAC investigators will seek to determine whether there is sufficient evidence to lay charges for breaches of the Prevention of Bribery Ordinance. It is understood the inquiry will focus on whether any party was offered an inducement to refrain from bidding. Under Section Seven of the ordinance, such an offence is punishable by 10 years' imprisonment and a fine of $500,000. ICAC Acting Assistant Director of Operations, Neil Maloney, said he believed the inquiry would be protracted and difficult because of the reluctance of many people to come forward with information. Investigators will also take possession of videotape recordings of manoeuvres on the auction floor during the bidding process. Mr Maloney said the ICAC had been obliged, in a departure from standard procedure, to make public their investigation because of premature publicity by a prominent Chinese-language newspaper. ''We are concerned about the blatant way it was seen to be done,'' Mr Maloney said of the auction on May 26. ''I think the whole tenor [of the investigation] is no different to the press articles that followed the auction; that it was a rigged auction, that a cartel was involved. ''I can say we received complaints from more than one member of the public. ''We want to establish exactly what happened at the auction. ''We basically need to find out as much as possible. We are also seeking any assistance from sections of the media. ''To date, we have received quite a degree of co-operation. But, it is not an easy inquiry to get into. It all depends on the level of co-operation. ''We have a dedicated team, headed by a principal investigator. We think it is a fairly important inquiry.'' It is the first time the ICAC has looked into alleged illegal behaviour at a public auction. Mr Maloney said complaints were lodged ''within a few days'' of the auction, where at least 12 developers appeared to combine to limit the price of a number of properties in Fanling and Yuen Long. At the time, real estate experts claimed the consortium paid $2 billion less than proper market value. The Secretary for Planning, Environment and Lands, Tony Eason, said there was nothing illegal in investors teaming up. After the sale - conducted at the height of government attempts to introduce restrictive measures to cool property prices - three of the territory's biggest developers denied they had attempted to exert any improper influence. New World Development chairman Cheng Yu-tung, Cheung Kong (Holdings) chairman Li Ka-shing and Sino Land chairman Robert Ng all denied suggestions that they had acted wrongly. Last month, a three-member panel appointed by the Government to review rules at land auctions, listed interim measures aimed at preventing a repeat of the incident. These included giving the auctioneer the right to withdraw any lot from sale and barring unnecessary audience movement. A new round of measures is expected to be made public later this month.