You can't fly any Drone over a crowd of people unless you have their consent, if you are flying 50 metres above people, you have to be fly the same distance to one side of them, and if you go higher bearing in mind the 120 metre altitude limit for any Drone in the UK ( expect with special permission from the CAA ) then you would also have to fly it 120 metres from them at ground level, so the higher you go the further you need to be away from people, if the Drone is less than 249 grammes then it only needs a operators registration again with the CAA, if it's over 249 grammes then it must have a pilot and operators registration clearly visible on the Drone itself.
There are quite a few restrictions, however the Sabs using them won't bother about that, I would just all stand there until the batteries are flat, normally about 25 to 30 minutes more power is used hovering than forward flight.