Four people were arrested today on suspicion of duping sport and music fans into buying tickets that did not exist.
The three men and a woman were held at addresses across London and in Waltham Abbey, Essex, on suspicion of fraud by false representation.
The move came after an investigation into a criminal gang that set up worldwidetickets.com and gigsport.com.
The two websites sold tickets for the Reading Festival and concerts featuring global stars such as the Black Eyed Peas and Michael Buble.
Evidence of the fraud emerged through 265 complaints by victims examined by the National Fraud Intelligence Bureau (NFIB).
They are estimated to have lost a total of £40,000, including a woman who flew from South Africa to the UK having paid £1,800 for three Wimbledon Centre Court tickets.
The NFIB was set up by the National Fraud Authority to receive nationwide reports from the public and small businesses.
Detective Chief Superintendent Steve Head, of City of London Police, said: "Without the bureau many more people could have fallen victim to a criminal gang who we believe to have already conned hundreds of people into paying large sums of money for non-existent tickets.
"I now look forward to police forces across the country using NFIB intelligence to track down the fraudsters who are destroying lives, damaging businesses and costing the UK economy billions of pounds."
Bernard Herdan, of the National Fraud Authority, said: "A case like this shows the importance of the public reporting fraud and how this contributes to an effective enforcement response."