“I do think things have a natural lifespan. 30 hours in this particular climate is a huge amount of episodic TV to deliver – and we did want to go out on a high.
“We wanted to do all the biggest stories that we could do, without petering out into something that just repeated itself.
“The brilliant thing was, once we did know it was going to be the last season, we could play to that. so instead of doing a rather unsatisfying ambiguous end, we knew we could do something extraordinary – which we have done.”