Thanks again. Now that puts a new complexion on things. Is exemption
granted automatically or does a higher authority need to assess the
situation?

Pls tell me, apart from removing the pump, cylinder and tank, will
pipes need to be changed to accomodate a new shower that is suitable
for a combi. I'm asking this because the bathroom is relatively newly
refurbished - so am I looking at quite a big job? Thanks.