Icstis fears people are unaware of premium calls' terms and conditions

The review by Icstis, the body that regulates premium-rate phone numbers, comes after a rise in the number of complaints about such services.

Even if unsuccessful, a phone call to such shows can cost some 75 pence.

Icstis wants greater transparency so callers know how much they are paying, and the likelihood of winning a prize.

Many people were unaware that even if their call are unsuccessful they would still be charged, and each time they redial they would be charged again, said an Icstis spokesperson.

'Teleshopping by stealth'

Quiz show calls have been an important source of money for TV channels, "replacing traditional revenue streams" in recent years, said Icstis.

While around 20% of the cost of a phone call goes to the provider of the phone network, the remainder is divided between the firm that operates the premium rate call system, and the content provider - in other words the TV channel.

"Some consumers have misunderstood the nature of the service or the charges levied regardless of whether they are unsuccessful in getting through to the studio," said Icstis in a report earlier in the year.

The review comes as telecom regulator Ofcom has started preparing proposals on guidance regarding the use of premium rates in television programming.

European legislation requires that advertising and programming is kept separate.

"Any consultation will be with the intention to ensure that such channels are genuine editorial channels and not teleshopping by stealth," said an Ofcom spokesperson.