I will defend the BBC here. The BBC is supposed to be impartial and objective, so that viewers can draw their own conclusions. So they try to avoid terms which seem to come with a moral judgement attached. One such term is "terrorist". They instead say "militant", because as one of their journalists said, "calling someone a terrorist means you're taking sides".
It's not the BBC's job to denounce developments in the news, or tell viewers what a moral outrage some piece of news is. The BBC's job is essentially "here is some newsworthy information that our audience might find interesting, and they can judge it however they wish".
I guess it's how the BBC retains public support. If the BBC became partisan and only represented the views of half the British population, the other half would call for it to be dismantled.
