Evening Standard's Londoner's Diary on English Pen

The Evening Standard has a short bit about all the actors singing "If I Had A Hammer".  You can read more about it here.

...the night ended with a surprising sing-song. Kingsley, with actors Matthew Macfadyen, Harriet Walter and Bill Paterson, took to the stage for If I Had a Hammer. “Ben must have been directed to  do the baseline,” says a PEN spokesman. “He was bobbing along singing bom-bom-bom-bom.”