Thanks for your advice, guys. We went for a Aqualisa Aquastream after
talking to our neighbour who had similar problems. This is the shower
that they eventually had fitted, so we know it can be done! They also
told us about the housebuilders' error with the hot and cold pipes
being in a non-standard position, i.e. the cold is on the right and hot
on the left, which meant that the crossed over pipes had to be boxed in
the wall behind. *sigh* Nothing's ever simple. Still, hoping to make a
start today. Thanks again!