Armitage, who will star as John Porter in Sky's upcoming series Strike Back, explained that he enjoyed returning to Spooks.
"It was actually quite thrilling and what's really interesting about Lucas this year is he's much less physical than he has been in the past," he said.
"It's almost as if, and not through choice, John's been out there doing all the fighting and Lucas is back engaging the cerebrum, if you see what I mean."
He continued: "It's a very interesting juxtaposition and I quite like that I've now got both those characters under my belt."
Strike Back will air on Sky1 HD in May.