I need an additional double socket in the kitchen. The socket will
supply a microwave (900w I think) and a deep freezer (about chest high,
not sure about rating).

The easiest solution in term of damage to the decor is to run a spur
from a nearby unused single socket that is on a very lightly loaded
ring. Alternatively I can add the socket to the same ring by
extending/crimping the cables feeding another socket of the above ring.
This however will result in quite a lot of damage to the decor that I
would rather avoid...

Any reason why not to use the first solution?