OG - the notion of a 'watershed' is an utter nonsense.
Does anyone seriously believe that in 2011, parents pack the kiddies off to be on the dot of 9:00 p.m. to shield their eyes from 'adult' content, and that anything shown before that should be as radical and progressive as The Wooden Tops.
With all the (constantly advertised by the BBC) 'view again' technology, re-runs and box sets of series, the idea that everyone watches TV at its broadcast time slot is simply ludicrous.
The fact that the government and media still use this stupid expression shows that thewy have patently failed to address the fact that media presentation and access is a universe away from where it was when the arbitrary '9:00 p.m.' rubicon was invented.