Former Interception Commissioner Sir Swinton Thomas said reports that British spies have access to millions of text messages were "a worry" and that he would have been concerned about this kind of use of foreign intelligence agency data.
– Former Interception Commissioner Sir Swinton Thomas
Certainly in my time I would take the view that it not open to our intelligence services to obtain or certainly to use communications or data which would not have been lawful in this country.
It's not dissimilar to the question of whether you use material which you may have reason to believe has been obtained by torture.
It's a different area of course, but the concept is very similar.