"Mandela was leader of the ANC's armed wing, Umkhonto we Sizwe which he co-founded. "he coordinated a sabotage campaign against military and government targets, and made plans for a possible guerrilla war if sabotage failed to end apartheid". If that's not terrorism (systematic use of violence as a means of coercion for political purposes) what is? The morality of this is another discussion.
> terrorism (systematic use of violence as a means of coercion for political purposes)
All warfare seems to fit under this definition. Commonly explicitly added qualifiers are "against civilians" or "by non-state actors". Another implicit one is "by people the speaker doesn't like".
I understand she was in power at the time. Cameron was linked however to this[1] 'hang Mandela' campaign poster. I'm not positive but I believe he apologised in parliament after Mandela's death.
I'm pretty sure that they both "considered Mandela to be a terrorist", and most of the rest of the Conservative party at the time did too. But at the time nobody cared what David Cameron thought.