I believe Robin was some way behind and was told "Stop or we'll shoot!" Basically he didn't fancy his chances.
The police are threatening that if anything like this happens in the future, the will shoot first and ask questions later. They reckon some al qaeda type might give it a shot in a superhero costume. Only in Britain!
Heard the big story of the day is protestors' getting into Parliment, same confusing breech of security as the idiots getting in the RNC Convention, several times!