As I have said before Cameron can not be trusted, but then there are few in politics that I believe can be. This will always be the case until there is true open and honest Government, which can only be achieved if there is a completely independent monitoring organisation of how the UK Government conducts itself and I can never see that occurring.
The general pubic and to some extent the Government are not aware of many of the activities of MI5 within the UK and MI6 outwith the UK. Some of these activites only become known, to some extent, many years in the future. The monitoring of Harold Wilson in the 1960s and 70s and Winston Churchil in the 1940s and 50s to name but two Prime Ministers. If they were not aware then these organisation could be up to anything.