Blue Peter will be banned from holding phone-in competitions after a BBC review found that it had conned thousands of children into taking part in a contest they had no chance of winning.

Mark Thompson, the BBC’s director-general, delivered a report on the operation of premium-rate services to the BBC Trust yesterday.

It detailed how, when the telephone system failed during a competition, a panicked researcher plucked a child from a Blue Peter studio “focus group” and fed her the correct answer. She was featured as the winner of the competition.

Blue Peter producers covered up the incident. At a production meeting three days later the researcher was congratulated for her “quick thinking”, the report said.

The Blue Peter team then allowed the rigged competition to be rebroadcast on CBBC, the children’s channel, with the phone-in number still on the screen, prompting a further 3,500 children to call in. Richard Marson, then editor of Blue Peter, has since moved to another job within the BBC.

Sir Michael Lyons, chairman of the BBC Trust, said: “The errors were serious as they resulted in children being misled to participate in a competition they had no chance of winning and in a child being involved in deceiving the audience. These grave mistakes were compounded by serious errors of judgment in not referring the matter to senior management.”

The possibility of technological error means that the BBC cannot guarantee that phone-in competitions can be run transparently and fairly within Blue Peter’s half-hour programme. Mr Thompson said: “We will suspend with immediate effect any further live telephone competitions.”

He said that the inexperience of the young Blue Peter staff was a factor in the incident and promised better training and a senior editorial figure on each BBC programme to oversee interactive elements.

Sir Michael said: “The culture of the BBC must be such that any proposal to mislead audiences is instantly dismissed as wholly inappropriate.” The suspension will not affect “vote-offs”, such as those on Any Dream Will Do.

The children’s department said that it used premium-rate services to cap the cost of call charges (typically at about 10p). The BBC does not take any profit from phone-ins.

Mr Thompson said that BBC phone-in competitions must have a “clear editorial purpose . . . Skill must be required to win when premium-rate lines are used, otherwise the competition may be illegal”.

The review also found that the cookery programme Saturday Kitchen misled viewers into believing that they were calling a live programme when in fact it had been prerecorded.

Viewers were asked to choose which pudding Ea-monn Holmes should eat “live”. However, Holmes was presenting a show on Radio 5 Live at the time. The trust criticised the Saturday Kitchen claim as “misleading”.

The BBC failures were uncovered during a series of phone-in scandals. Investigations by Ofcom and Icstis, the premium-rate regulator, are continuing.

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