Unless the wiring is in a steel tube.

Not 100% sure of the top of my head but I think it can be any suitable metal protection. Look it up on the Part P Website. http://part-p.org.uk/

But you will be fitting RCD's anyway won't you?

You don' have to at all, but there are other rules that make it harder and more expensive to meet compliance. They are such a simple and cheap option. Keep the lighting circuits separate though as you may well need light if an RCD goes and it disconnects the lights, think this is covered in Part M but worded differently.
The 17th Edition is being updated and it may well be worth, if you got the time, waiting until next year so that you can comply with the very latest regs. Though I suspect as it is 'only' another 50 pages it will be minor things like energy efficient light fittings.

Hi all, thanks so much for your contributions..very much appreciate it.

Getting quotes from architects now to design the plans for permission. With building regs plans, a builder friend says you can just get a building notice so no need for plans just carry on and let them inspect regularly. Has anyone got any experience of timber framing with a building notice?

evan, like the look of those new building systems. Will look closer. I quite fancy making the panels thinner, then using wood fibre batts inside the gap between panel and plaster board to give a little thermal mass and to vary the insulation...Will look into that.

I also have a huge amount of rockwool loft insulation left over from doing the loft which I feel I could use in some way as I've already paid for it. Anyone know if I can use rockwool in the gap with wiring? Would it be effective/complicated/stupid to use it?