The only way I can get the kitchen layout to work is to install the
electric hob above the washing machine. I can see it's not ideal, but is
it allowed? Any extra precautions I could take, eg install some sort of
vapour barrier?

I personally can't see why it is any worse than installing it under a
food preparation counter-top, which is what most of us do.
--

Graham.
%Profound_observation%