You're right PaulB, some years ago an undercover newspaper report found out that the celebrities sometimes had earpieces to help them along. The Countdown production team didn't deny it either - they said that they'd never suggested that that wasn't the case and that it was only given to some celebrities because the recording demands were so rapid.
Richard Whitely said himself on one online chat interview last year: Occasionally they do come up with long words because [the celebrities] are highly intelligent. They do have an earpiece, which is connected to the 2 producers, Damian and Michael, who play the game in the gallery, so they offer those words to them. It's not cheating, but obviously if you think about it you've got to offer the best possible solution that you can otherwise it would be a pretty dull game. The job of those people is to add value with the spin that they put on the words. It's no secret, we've done it for 21 years. We could have Damian and Michael in Dictionary corner but it would be less pretty!