The Civil Aviation Authority have responded helpfully and comprehensively with chapter and verse.
The full response is here, http://www.whatdotheyknow.com/request/1 … Letter.pdf but they summarise at the end:
In essence therefore, provided the aircraft has a mass of 20kg or less, the current regulations state,
The operation must not endanger anyone or anything
If the flight is to be conducted within 'Controlled' Airspace, or within the ATZ of an airfield (the dimensions of an airfield ATZs vary, but have encompass the airspace within either a 2nm or a 2.5nm radius of the airfield) permission to fly must be obtained from the ATC unit/authority and the flight must be operated in accordance with that permission and any additional restrictions required by ATC. Obviously therefore, there is an inference that the 'pilot' needs to have a degree of awareness about the airspace that he/she wishes to fly in.
The aircraft must be kept within the line of sight (500m horiz, 400ft vert) of its pilot'. Operations beyond these distances must be approved by the CAA (the basic premise being for the operator to prove that he/she can do this safely).
Small unmanned aircraft (irrespective of their mass) that are being used for surveillance purposes are subject to tighter restrictions, which invariably will require permission from the CAA before operations are commenced
CAA permission is also required for all flights that are being conducted for aerial work (ie. you are getting paid for doing it)
The 'pilot' has the responsibility for satisfying himself that the flight can be conducted safely
Basically: Don't fly near an airport. Keep the drone in sight, and within 500m laterally / 400ft height (which is basically mandated by the software / Wifi connection anyway, unless using mirumod!). You're responsible for any stuff-ups and resultant consequences. Beyond that, as long as you're not conducting surveillance or paid work with it, do as you want.
So there you go