Jacko,
Dredging up that stuff I learnt from OS lectures, I think that surveillance is general, routine observation of a large area. Reconnaissance is more specific, targeted information gathering. To use a naff photography analogy, surveillance is a wide angle lens, reconnaissance is a telephoto zoom lens. 'Intelligence gathering' is a far more general term for what agencies such as JARIC or SIS do. They use sources to provide information. Information is classed as 'raw material', it has to be processed and given some type of predictive value by analysts, when it then becomes intelligence as opposed to information. Intelligence can be roughly divided into 4 categories: Imagery Intelligence (IMINT-looking at pictures), Human Intelligence (HUMINT-agent handlers meeting agents), Signals Intelligence (SIGINT listening and decoding communications and emissions) and Open Source Intelligence (OSINT-Jane's the internet and 'papers). Hope the above didn't get too patronising/geeky, feel free to email any more specific qeuries.