Hi Caroline,
Your plumber is giving you the wrong advice... your bath is much bulkier than the wash basin or even the WC, so better where it is now - I think you are stuck with this layout, unless, as others suggested above, you turn the bath into a shower cubicle. If the floor joists are running from back to front (parallel with your current bath) then your builder might be able to run a new soil vent pipe in between two joists, thus you could have your roll top bath... Just a thought. Irina
Q
Love the colours
Q