On song: X Factor's Joe McElderry turns on Regent Street's Narnia-themed Christmas lights

By JODY THOMPSON Switched on: Last year's X Factor winner Joe McElderry performed his son Ambition before turning on London's Regent Street Christmas lights Thousands of screaming fans wrapped up warm to see last year's X Factor winner Joe McElderry switch on London's Regent Street Christmas lights last night.The road was cordoned off for the event, which saw Joe perform his single Ambitions and