I have 3 double sockets and a TV point on my chimney and they were put in by eletrician within past year who seems fairly up to date with legsilation - never actually asked him if ok, he just did them......
The only reference I can find to your dilemma is Part J of the Building Regulations, Diagram 2 which states that combustible material (electrical cables, etc?) must be separated from a flue by solid, non-combustible material of at least 200mm thick.