The news came as the regulator of premium-rate phone services, Icstis, announced it would introduce a licensing regime within three months for programmes that useviewer phone-ins.

Five suspended all its premium-rate phone services yesterday. Its lunchtime show Brainteaser had asked viewers to solve a word puzzle within five minutes. But when the audience failed to get the right answer, names of winners listed on screen were simply made up. On one occasion, a member of the production crew went on air posing as a "winning contestant".

The quiz is produced by Cheetah Television, a subsidiary of Big Brother makers Endemol. The deception came to light after Five - which knew nothing of the scam - began a review of its premium rate phone-ins.

Five's chief executive Jane Lighting said: "We are shocked and disappointed and wish to apologise unreservedly."

Sir Alistair Graham, chairman of Icstis, acknowledged that public trust in premium-rate phone-ins had been damaged in the wake of a series of revelations.

He said Icstis would refer evidence of a criminal offence to police. But Sir Alistair said there was no evidence of any "cover-up" of the problem by broadcasters.

Earlier this week, ITV suspended all its phone-in shows pending a review.

Icstis said it is investigating six shows: Channel 4's Richard and Judy, the BBC's Saturday Kitchen, and the ITV shows X Factor, Ant and Dec's Saturday Night Takeaway, Soapstar Superstar and I'm A Celebrity.