Having now decided on the WC extractor (thanks to PeterC) it's time to
tackle the next problem.
My cooker is set into what was once the kitchen fireplace. To reduce
noise in the kitchen I plan to fit a S/S box (about 1100 x 300), with
appropriate filters, in the space above the cooker and to extract
(horizontally) through the side chimney breast and a 90 degree bend,
then through the wall to the outside world. The ducting run would be 1-2
metres and there are no neighbours to worry about.
It would be great to hear from anyone who has done something similar.
The decisions are whether to have an externally-mounted fan or an
in-line fan, where to buy, and whether the S/S plenum is available or
whether it needs to be bespoke. Google has turned-up a few possible
candidates but opinions based on personal experience are always useful.