It's one of television's most successful shows ever and this year's series was meant to be all about celebrating its 20th anniversary.   But controversy has hit the BBC dancing contest in recent weeks. Two male dancers have left the show amid allegations of misconduct, and last week it was announced production staff will chaperone all rehearsals from the next series.     The BBC's annual report was released today and its director-general Tim Davie apologised as he addressed the Strictly controversy, saying the corporation "will never tolerate unacceptable behaviour".   Host Niall Paterson is joined by our entertainment correspondent Katie Spencer and TV critic Scott Bryan to discuss how the BBC has handled the crisis and Strictly's future.  Producer: Rosie Gillott Editor: Wendy Parker Promotion producer: David Chipakupaku