In recent years there’s been a fashion for arts documentaries presented by celebs rather than boring old experts — presumably on the grounds that knowledge and insight are no match for vague enthusiasm and a touch of showbiz glamour. (In a particularly gruesome episode of ITV’s Perspectives, Pop Idol winner Will Young established his credentials for discussing the life and works of René Magritte with the words, ‘I’ve been collecting bowler hats for 12 years now.’)