In a case of "Just because you're paranoid Don't mean they're not after you" Harold Wilson, who was paranoid about lots of things but particularly being bugged by MI5, was in No 10 at a time when there were bugs in cabinet room and PM's study - whether the bugs were actually used or not isn't known:

http://en.wikipedia.org/wiki/Harold_Wilson_conspiracy_theori...

Edit: If anyone is interested in this stuff, I can strongly recommend Dominic Sandbrook's histories of the UK in the 60s and 70s:

http://www.amazon.co.uk/Dominic-Sandbrook/e/B001HCWSSW/ref=n...