A TV quiz channel changed answers to avoid paying big prize money and left phones unanswered to wring more cash from premium rate numbers, a whistleblower claimed yesterday.

Robert Winsor, an ex-call operator for Big Game TV, told a Commons select committee how he took calls in October 2005 on a game asking for "things you see in a pub".

He explained: "The top answer 'pork scratchings' was worth #200 and a winner guessed it within the first 30 minutes of the game.

"When the top prize is won this quickly, it is not good for call revenue as having a top answer of #200 still to be won is more tempting to viewers than a #20 bottom answer.

"Bearing this in mind, the producer moved this top #200 answer down to the #40 answer slot while the presenter stalled the player with the usual, 'Hi! So, where are you calling from?' chitchat.

"The producer entered 'drunk person' as the new top answer, thus depriving the winner of #160." He also claimed he was told to take a break and leave the phone unanswered when viewers were in danger of getting a top answer. Ofcom is investigating Winsor's claims.

Calls cost at least 75p per minute - even if callers fail to get through.

The committee's report revealed cases of an individual charged #348 for 15 calls and a parent whose son and his babysitter ran up unauthorised bills of #700.

TV Quiz shows should to tell callers their odds of getting through, the committee said. It concluded TV quiz shows "look and feel like gambling" and called for tougher regulation.

In the past two years, broadcasters have been making up for lost revenue from falling advertising through quiz TV channels. ITV Play made more than #9million in profits in the first half of last year.

ITV said: "We've already taken steps to ensure that viewers are always able to make fully informed choices about participating."