Nice spa in London for day out with pregnant friend - any recommendations?

[treacletart]

My mate wants to treat her pregnant friend. Any ideas that won't break the bank?

Bumping for you.

I tend to end up at the Sanctuary. It is stuffed to the gills and can feel a bit crowded but nice in that you can spend a day there wafting about (two swimmimg pools, two whirlpools etc.). If she is pregnant then she won't be able to go in most of the heat treatments, so a decent pool is a good idea. They do special pregnancy treatments too.