If I already have a bathroom on the second floor of my town house, are the floor boards/house structurally sound enough to replace the shower with the weight of a bath? Persimmon home, uk, 2007 built

If you already have a bath upstairs and wish to add a bathtub,( Metal, plastic, steel or cast iron?) the changes are good that your tub won't come crashing down in the living room on top of the telly. Good luck in your project'
Here in the plumbing page we do our very beat for out British friends, Tom

Usually, second stories are built to withstand weight of bath tub. As Tom suggested above, you should be OK with installing tub in place of shower. Milo