That bathroom thing is a pain. You'll need to get a regularisation certificate from your local bui;ding regs department (see the council's website). I think the fee is about £140 and you have to fill out some forms and get the new bathroom inspected to make sure it complies (and if not they'll prescribe some work that needs doing before they can approve the change). A bigger hassle might be getting the freeholders permission for the conversion, but your solicitor should be able to deal with that. The good news is that I don't think bathroom moving requires planning permission (I moved a kitchen in a flat a few years ago and that was just building regs, not planning permission).
Hope your day's going OK otherwise. Try not to overthink the situation- there are no answers!!
