Singing for Syria: Robbie and Lily (as you've never seen her) at Unicef's Halloween fundraiser

Lily Allen and Robbie Williams performed at a star-studded bash for Unicef last night as Jodie Kidd, Ewan McGregor and Sophie Dahl dressed up to do some good on fright night.

The Unicef UK event in central London was also attended by Ewan McGregor, who has been one of the charity's ambassadors since 2004.

The actor said the plight of children in the war-torn country was "unfathomable".

"The situation is continuing to get worse and worse and there are more and more children who need our help and assistance," he said.

"So it's really important that it's kept in the public's consciousness, that we don't forget."

Fellow Unicef ambassador Jemima Khan, who was dressed as the main character from the film Black Swan, was hosting the Mayfair event.

"Four million children are estimated to be in the greatest need at the moment," she said.

"It's considered to be the greatest refugee operation in history, the biggest humanitarian crisis that they've had in many years."

Nesbitt, who wore a plain suit but added a touch of horror by wearing contact lenses which turned his eyes black, said it was "amazing" that the Government today pledged to match every pound raised by Unicef for the cause.

To back the campaign by donating £5, text "Syria" to 70007.