Regulations

Summary of UK legal requirements

The aircraft must not be flown:

over or within 150 metres of any congested area
over or within 150 metres of an organised open-air assembly of more than 1,000 persons;
within 50 metres of any vessel, vehicle or structure which is not under the control of the person in charge of the aircraft
within 50 metres of any person except during take-off or landing, the aircraft must not be flown within 30 metres of any person except for the person in charge of the aircraft.

The Dronecode

Make sure you can see your drone at all times and don't fly higher than 400 feet
Always keep your drone away from aircraft, helicopters, airports and airfields
Use your common sense and fly safely; you could be prosecuted if you don't.

Drones fitted with cameras must not be flown:

within 50 metres of people, vehicles, buildings or structures
over congested areas or large gatherings such as concerts and sports events

A useful link to UK regulations.