I had this situation exactly with a client in November who has three phase power and an old Stone/Brick traditional farm house that has grown into a 6 apartment complex.
Powerline adapters would just not work! The three phase system and old wiring/switchboards just would not let the units talk to one another.
Power surges can also be a problem and I have heard of cases where signal quality decreases if the powerline units overheat.
I thought they were a good solution for this type of problem.
As regards using UK ones, they should work with a three pin to two ping adapter.
Lidertronica in Lisbon have a wide range of network and other hear. They deliver COD by cobrança.
The relevant page on their website with links to powerline adapters is here:
I have just bought an external 10dbi omni-directional wifi antenna from them to mount on the roof of the above-mentioned client's house.
I plan to bathe the complex with wifi radiation and as well as ensuring good coverage, add to the tans of the punters regularly staying there!
If it is in stock they deliver the next day.