Giles Clarke, the chairman of the ECB, has revealed that as many as 700 unauthorised websites providing illegal streams of cricket matches have been closed down, and has warned that they are "the biggest danger" facing the game.

Clarke made his remarks on Test Match Special after the ECB confirmed a new six-year deal with the BBC to provide live radio coverage of England's home internationals. The agreement, which covers all forms of the game, will run from 2014 until 2019.

The ECB is also thought to be close to agreeing a new television contract with Sky. The current £300 million, four-year deal expires at the end of 2013 and it is regarded within the ECB as essential to the survival of the 18-county professional circuit.

Clarke said he was concerned by unauthorised websites providing illegal streams not only because they undermined rights deals but also on the grounds that they affected the fight against corrupt betting activities.

"We all have to be very vigilant," he said. "There are a huge number of pirate websites streaming cricket on the internet taken from television broadcasts. We and our broadcasters closed down 700 during last summer's series against India. It's an extremely complex procedure, but it can be done and it has to be done.

"That is the biggest danger to cricket, because they take money out of the game without commercial benefit to us. They are being used by the bookmakers as well. The problem of pirate-site streaming is very big for sport."