Thanks for the advice Andrew. Unfortunately SWMBO insist on a heated
towel rail of some kind. After posting I had a thought that I could
simply purchase one of those dual powered rails so I could plumb this
into the CH system so it will be on in the winter, just like a normal
rad, and in the summer we could rely on the heating element. Thinking
about this some more I'm not so sure I would need it on in the summer
at all this could just be wasted effort on my part. Also the wetroom
willl have UFH as its primary heat source.

Cheers

Richard