Re. The powerline adapters.
Are they effective if you plug into into an extension block ?
The D-link ones I bought my parents work fine in an extension block.
However, the instructions don't recommend it, (but don't explicitly state they won't work) and recommend using 'passthrough' Homeplugs, i.e ones with a socket integrated into them if you're short on sockets.
They won't work if the mains block has any filtering/surge protection though.
Just discovered Sky do a wireless connector.
All my wireless bits work well so it was just for getting the signal to the Sky box.