"In each episode of the show, host Noel Edmonds invites viewers to call in to win either £1,000, £2,000 or £15,000. The prize is determined by a box opened at random at the end of the show. However, as the programme is pre-recorded weeks in advance, producers are already aware of the prize when they advertise the competition.

The regulator's spokesman added: "How can the producers say you can win three different amounts, if they already know which box has been selected? Obviously if only the minor prize is remaining, you can't advertise the ­bigger prize. That's misleading."

http://www.digitalspy.co.uk/broadcasting/a46205/c4s-deal-facing-phone-in-investigation.html

i really thought this is a live show,so they are also cheating by asking you to call to get an unknown prize money which they already knows

All game shows and phone-ins are a scam, one way or another :). You don't get nothing for nothing...

Or "something for nothing", perhaps?
I've always found that if I have nothing in my pocket, then I can always buy nothing. In fact I can get so much nothing with my no money status, that it's difficult to get it all home.

Now there's something.

Yes, perhaps that was the quote I was looking for at the time... obviously you won't get nothing for nothing... but something for nothing, yet another thing highly unlike to happen :).