Widespread suspected match-fixing exists at the top level of world tennis, including at Wimbledon, according to secret files obtained by the BBC and online BuzzFeed News.

Over the last decade, 16 players ranked in the top 50 have been repeatedly flagged to the Tennis Integrity Unit (TIU), which was set up to police the sport, over suspicions they have thrown matches, the news organizations said.

All of the players, including winners of Grand Slam titles, were allowed to continue competing. Eight of the players are due to play in the Australian Open which starts on Monday, they added.

The BBC and BuzzFeed News said they had not named the players because without access to their phone, bank and computer records it was not possible to determine whether they took part in match-fixing.

The TIU did not immediately respond to a request from Reuters for comment.

The BBC and BuzzFeed News quoted Nigel Willerton, director of the TIU, as saying: "All credible information received by the TIU is analyzed, assessed, and investigated by highly experienced former law-enforcement investigators."

The news organizations said they had obtained a cache of documents that included the findings of an investigation set up in 2007 by the organizing body, the Association of Tennis Professionals (ATP).

The documents show the inquiry found betting syndicates in Russia, northern Italy and Sicily making hundreds of thousands of pounds betting on games which investigators thought to be fixed. Three of these games were at Wimbledon.

In a confidential report for tennis authorities in 2008, the inquiry team said 28 players involved in those games should be investigated but the findings were never followed up, the news organizations said.

Tennis authorities introduced a new anti-corruption code in 2009 but after taking legal advice were told previous corruption offences could not be pursued, they added.

In later years there were repeated alerts sent to the integrity unit about a third of these players. None was disciplined by the TIU, the BBC and BuzzFeed News said.

The BBC and BuzzFeed News were also given the names of other current players they said the TIU has repeatedly been warned about by betting organizations, sports integrity units and professional gamblers.