Customers of the world's leading betting exchange, United Kingdom-based Betfair, must agree to allow confidential information to be passed to racing authorities from tomorrow or cease to use the site. Betfair, as well as its much smaller UK-based rival exchange Sporting Options, yesterday released details of a deal reached this week with the English Jockey Club aimed at allaying integrity fears over jockeys or trainers backing their horses to lose. In January, this possibility moved Hong Kong Jockey Club's executive director of racing, Winfried Engelbrecht-Bresges, to call exchanges 'the biggest threat to horseracing's integrity' worldwide and to call on racing jurisdictions everywhere to influence governments to ban their use. Despite this latest news, he remained sceptical yesterday. 'I think this is a good move and one has to acknowledge the willingness of the Betfair people to address this integrity issue and to co-operate with the authorities, although there are exchange firms who have not agreed to this,' Engelbrecht-Bresges said. 'However, we still have to consider that the name of the account might not be the name of the one having the bet. And this agreement does nothing to alter the principle that giving people an outlet to bet against their own horses winning makes handling integrity and especially the perception of integrity almost impossible.' Betfair's statement to customers explained that details of bettors' names and specific betting patterns may be passed on to racing officials 'only in certain circumstances' to facilitate investigations into alleged corruption. 'The changes are designed to allow Betfair to share information and co-operate with sports' governing bodies if there is good reason to believe that there has been a serious breach of their rules,' Betfair said. 'We believe this to be important to preserve the integrity of sport and our customers have nothing to fear from these amendments.' Customers logging into these exchanges from tomorrow will be asked to accept the new terms and conditions and will be unable to use their accounts if they do not accept them. However, Betfair reassured customers that 'there will have to be highly suspicious circumstances' and 'the Jockey Club will not be able to come on a fishing expedition, randomly casting around for information'.