OP,
FWIW:
If possible the Dremel method, as suggested above, is perhaps the way to go.
Dont use any kind of flame under or above the bath.
If you have slightly larger dimensions than typical for the back nuts then you could file or grind down the jaws of a cheap (£3 say) basin wrench until they are open enough to fit the back nut.
Cutting off the tap head (with an angle grinder) and drilling down to burst the back nut was a common method of removing taps almost welded fast with red lead, paint and putty.
FWIW:
If possible the Dremel method, as suggested above, is perhaps the way to go.
Dont use any kind of flame under or above the bath.
If you have slightly larger dimensions than typical for the back nuts then you could file or grind down the jaws of a cheap (£3 say) basin wrench until they are open enough to fit the back nut.
Cutting off the tap head (with an angle grinder) and drilling down to burst the back nut was a common method of removing taps almost welded fast with red lead, paint and putty.
