Gareth Malone has admitted that he has been banging his head against the wall while attempting to get a "decent sound" from the celebrities in his Children In Need choir.

Strictly Come Dancing judge Craig Revel Horwood, Great British Bake Off host Mel Giedroyc and former footballer Fabrice Muamba are among those singing a cover of Avicii's Wake Me Up for the charity.

Their rehearsals have been captured in a two-part TV documentary for BBC One.

Gareth told Radio Times magazine: "There have been moments of banging my head against the wall. I would hate to be mean because they've all worked so hard. Yes, if I were auditioning, most of them would not be the first choice for any choirmaster - but that's the point.

"We are putting this out as a record and we want people to buy it so it can't sound dreadful. It's been a lot of work to get them listening to each other and making a decent sound."

He said that the usually acerbic Craig shook as he auditioned for his solo.

"I have to say, I couldn't help but enjoy seeing the boot on the other foot: the scary Strictly judge quivering and quaking as he auditioned for a solo," the choirmaster said.

And Mel added of the Strictly judge: "I can reveal that Craig Revel Horwood's right leg was shaking uncontrollably."

She admitted: "Standing up and singing on your own is terrifying. You feel as if somebody has stripped you of all your clothes."

Gareth, who has previously topped the singles chart with his Military Wives choir, s aid that he had to "have words" with comic Jo Brand because she was being the "class clown".

Of presenter John Craven, who is also in the choir. he admitted: "I'm waking up in the night, worrying about John... Poor John was very, very nervous about singing. He also tends to be one beat behind: 'Where are we going from again?' he's been heard to say!"

He said that Muamba had been producing "something quite sensitive" but of former Gavin And Stacey actor Larry Lamb, he added: " He's... a bit of a crooner. I've had to ask him to tone it down. Unless you're doing a solo, you don't want to stick out too much."

Children In Need last topped the charts in 2010 with JLS's Love You More.