I am installimg a shower to the end of the bath tup with a single mixer for both the shower head and the bath spout
What is the correct height above the bath and dose it go to the centre or is it offset to the centre of bath

Hi Sam

No exact rules here. For tub/showers, I always install my mixer valves at about the belly button height of the tallest person in the house. You would then want to center the mixer and the shower head to the center of the drain.

With that being said, however, the manufacturer of the mixer will have specific recommendations so read the instructions provided with the mixer and then decide how you want it set up, OK?

Mark