Its a bit of a long process, but you need to contact your electricity provider. Try to get through to the 'Networks' (as I have been told,) department, and they should be able to tell you what type of earthing system would have been on your house if any. I have encountered this problem quite a few times, or the existing earth is not up to standard etc. You really should get this done before you have any work carried out. If you live in a rural area, where your supply comes in by 'telegraph' poles, you may have what is known as a TT system which your electrician will know about, and they can provide a suitable earth for you. As for the RCD or RCCD consumer unit, they vary in price. A little tip is that and I didnt tell you this, but B&Q warehouse sell a Wylex 'split load' consumer unit with MCBs and spare sockets for just under �70. That really is a good price, and will cover most general households, but may need the odd MCB or so for other equipment you have installed. If again you live in a rural area and do have a TT system, then expect at LEAST double that price as you will need a specific RCCD 100amp 100milli-amp to cover your entire system, then a suitable 30ma RCD for your sockets, external equipment etc. As for your bathroom electrics, your electrician is right you REALLY do need a good earth return path to try and cover every electrical appliance and mettalic parts as possible just to be on the safe side. Good Luck hope it helps