What are the rules in UK law on carrying dangerous goods on drones?
Article 94 of the Air Navigation Order


  (1) A person must not cause or permit any article or animal (whether or not
  attached to a parachute) to be dropped from a small unmanned aircraft so as to
  endanger persons or property.
  
  (2) The person in charge of a small unmanned aircraft may only fly the aircraft if
  reasonably satisfied that the flight can safely be made.
  
  (3) The person in charge of a small unmanned aircraft must maintain direct,
  unaided visual contact with the aircraft sufficient to monitor its flight path in
  relation to other aircraft, persons, vehicles, vessels and structures for the
  purpose of avoiding collisions.
  
  (4) The person in charge of a small unmanned aircraft which has a mass of more
  than 7kg excluding its fuel but including any articles or equipment installed in or
  attached to the aircraft at the commencement of its flight, must not fly the
  aircraft:
  
  (a) in Class A, C, D or E airspace unless the permission of the appropriate air
  traffic control unit has been obtained;
  
  (b) within an aerodrome traffic zone during the notified hours of watch of the
  air traffic control unit (if any) at that aerodrome unless the permission of
  any such air traffic control unit has been obtained;
  or
  
  (c) at a height of more than 400 feet above the surface unless it is flying in
  airspace described in sub-paragraph (a) or (b) and in accordance with the
  requirements for that airspace.
  
  (5) The person in charge of a small unmanned aircraft must not fly the aircraft for
  the purposes of commercial operations except in accordance with a permission granted by
  the CAA.


So section 3 states you must have direct visual contact and section 5 states that you must get permission from the CAA


  
    An individual or organisation that would like to conduct regular flights with their drone, however, will probably need to submit an
    operating manual to the CAA for a permanent approval. This will allow
    greater freedom to operate continuously without the need to seek ad
    hoc approvals.
  
  
  This type of Permission could be of use to:
  
  emergency services a local authority that would like to use a drone to
  carry out maintenance inspections of its property As with a Permission
  to carry out a commercial operation, the CAA will need to be assured
  of the competence of the person who will be flying the device. The
  ‘pilot’ therefore will probably need to undergo an assessment process
  with one of the approved National Qualified Entities.


http://www.caa.co.uk/Commercial-industry/Aircraft/Unmanned-aircraft/Unmanned-Aircraft/