The Channel 4 show, presented by Noel Edmonds, came under question when viewers spotted that one of the cash amounts vanish from the on-screen graphics board - before the box containing it had been opened. Edmonds regularly insists that only an "independent adjudicator" is aware of which figures are in the sealed red boxes.

The Sun reports that on last Friday's show, prior to the contestant's chosen box being opened, the £100,000 graphic disappeared - only to reappear seconds later. However, it vanished for a second time when it was revealed to be the amount in the chosen box.

"The whole point of the show is that no-one knows what is in the boxes," one viewer told the paper. "But by the look of this, it seems that the production team knows exactly what is in them before they are opened. Someone gave the game away by being a bit too quick off the mark with the graphics."

However, the show's producers blamed the slip-up as a "post-production error", claiming that the graphics had been added following filming of the episode.

A spokeswoman commented: "The on-screen money amounts are added after the show has been filmed as part of the post-production process.

"Occasionally, an error is made in the overlay and this is quite simply down to human error."