BBC Editorial Guidelines.
"Our policy is about achieving consistency and accuracy in our journalism. We recognise the existence and the reality of terrorism - at this point in the twenty first century we could hardly do otherwise. Moreover, we don't change the word "terrorist" when quoting other people, but we try to avoid the word ourselves; not because we are morally neutral towards terrorism, nor because we have any sympathy for the perpetrators of the inhuman atrocities which all too often we have to report, but because terrorism is a difficult and emotive subject with significant political overtones."
http://www.bbc.co.uk/editorialguidelines/page/guidance-reporting-terrorism-full