Contestants on the show choose nine letters and then have 30 seconds in which to use them to come up with the longest word possible. Although the celebrities do not compete in the quiz itself, they sit in 'dictionary corner' and try to come up with better answers than the contestants in the same time.

Speaking on BBC Radio 5 Live's Late Night Live, Mr Parris, who has been a celebrity guest on the show, revealed that he had been given an ear piece with a hotline to the show's behind-the-scenes experts who fed him the best words.

A spokeswoman for Channel 4, which screens Countdown, said celebrity guests in dictionary corner were "sometimes given a helping hand" during the show.

"Celebrities will come up with their suggestions but there is a team in the gallery who supply extra ideas," she said.

'Clever' celebrities

Mr Parris said: "I was pleased with the help as I would have been struggling without it. I used to wonder why the celebrities were so clever - and now I know."

A spokeswoman for Yorkshire TV, which makes the show, denied that viewers had ever been duped.

"We have never tried to hide the fact that the two people in dictionary corner have earpieces. The people in the audience are aware of that," she said.

The show's presenter Richard Whitely said: "We have to give the audience, we feel, the best available words that can be got in the time.

"If people were getting five and five, people at home could be getting six, seven and eight, or even nine, and we have to have an end product.

"There's been no secret about it because in former years there were ear-pieces with great long wires and for people with baldish heads you could see the wire going in," he said.