Presenter Darren McMullen is bracing himself to step in for the forfeit on Saturday’s The Magicians because the losing celebrity might not have the nerve.

The host of the BBC1 show – watched by around six million viewers – is on stand-by in case the chosen star is too scared at what is being billed as the show’s scariest challenge.

So far celebs have had to face nailbiting live stunts such as walking on broken glass or having an apple shot from their head with a bow and arrow.

Producers are keeping the details of the final forfeit secret, but say it is the ‘most terrifying yet’.

The final programme of the series will see George Sampson, Ed Byrne and Joe Swash pair up with the show’s resident illusionists. The team which gets the least public support has to face the forfeit.

A spokeswoman for the show said: “It is genuinely the scariest thing we have ever done in the history of the show. Darren has always been warned that if a celebrity feels unable to complete the forfeit that he has to step forward to do it…

“We’ve left this forfeit to the last one in the series in case we put off some of the other celebrities. We can’t give away precisely what the forfeit is, but needless to say it involves a big element of genuine fear – it will terrify the celebrity magicians.”

Darren said: “During this series of The Magicians I’ve been very lucky to avoid the forfeits as all our celebrities have been incredibly brave and faced them. However we have Joe Swash on this week’s show so it might be my time to step up to the plate if he or the other contestants chicken out.”