I'm no expert on the regs, but it is possible that the current regs don't _require_ additional bonding in your bathroom even if it was at one point necessary. There does need to be bonding where the water main enters the house - and you should get someone to check the 'seems to have been disconnected' wire to see that there really is something on the other end of it, and then to connect it. The concerning scenario would be that someone removed it to stop an RCD tripping, implying there is an underlying fault which could easily become dangerous.
With a non-trivial install, a real electrician is a better gamble than a EV retailer. Our BP install was 'ok', but not pretty.
