In one episode of the iconic British sitcom Only Fools and Horses, the street-sweeper Trigger tells Del Boy and Rodney that he has had the same broom for 20 years. They are amazed. Yes, he explains, the same broom – just with 17 new heads and 14 new shafts. Trigger insists it is the same broom. Del Boy thinks he’s barmy. Who is right?