Lots of replies since I last looked - thanks for all the feedback.
dingbat - yes, fair points. In this instance, the bathroom was planned (and bits ordered) way back. I'd had a number of issues with the various options for installing a shower, and the choice of electric was a compromise and late in the day - hence the electrics being seen as a painful addition to money already spent. I.e. I want a 45amp line for a shower = probable lighting circuit rewire.
The problem I guess is that if you asked someone whether they'd want to spend money or get an electric shock (or have their house burn down) then they'll spend money. However, if you ask people whether they want to spend money on perceivable, tangible benefits (such as a new bathroom) or spend on something they can't see, don't really understand, but should probably reduce the statistical chance of them possibly being electrocuted or their house burning down at some possible point in the possible future... well, you can kinda understand why people do it (and smoke, and play the lottery etc.)
I think, from other work I've done before, that I could do the wiring, but I don't have the regulation test equipment. I've still got to wait for the guy to turn up and have a look at the place, but if he says a rewire is necessary then I'll probably do the work of getting all the upstairs floors up. Hopefully that should reduce the cost, as he's then 'only' got to replace the wires (ignoring the joys of getting the wires out and back into the walls of course).
Paul_C - yes, I bet that was the exemption for originally not earthing the lighting: no metal fittings + non-conducting floor.
mikhailfaradayski - it wasn't an assessment of safety, more an mixture of annoyance and resignation
wingcoax - good question. I will have another look, but I'm pretty certain the grey sheathed cable was just big enough to carry the red & black insulated wires - not much room for even a bare earth wire.
RF Lighting - good thought, and one that I really hope is the case. I could isolate the lighting circuit and have a check. It would make the job for the sparky much easier. Though I guess all those grotty wooden back boxes will still have to go (I love the idea of using a flammable - though admittedly non-conducting - material to enclose electrical wiring)
ban-all-sheds - Alas an idiot has done something daft with the mains wiring in the kitchen. That was always planned for a full rip out and fix by a professional. My thinking at the moment is to get the whole lot done in one go, and accept a mess in the kitchen until I've got the time and finances to decorate. That's the pain - if the new regs had been in force when he sold the house, he'd have had his backside kicked and been made to pay to fix it. Unfortunately, it's going to be me that pays to fix it! Who said life was fair