Firstly, treason is the only crime in the UK which still carries the death penalty as I understand it.
Secondly, before we all get 'gung ho' and race for the kangaroo court, those arrested may only have been 'mules'. More dangerous in my mind are those behind the plots who recruited the bombers and could find another four clowns in the UK. Anyway, at least the residents of London should sleep a little more easily tonight.