Supply Pipe

I need to re-route our water supply pipe as the room it used to enter the house in has been demolished. I've located the existing (cast iron) pipe at a suitable point underground, so need to route from there, under the external wall and up through a suspended floor into the kitchen.

I've already had a thread on how to connect onto the pipe, but now I have a couple more questions:
- Regs state that the pipe should be 750mm below ground level, but the existing pipe is nowhere near that - more like 400-500mm. Do I need to route the new pipe down or just keep the existing level?
- Regs also state that I need to protect the pipe as it goes under the house, and insulate it. What do I use to do this? Apparently I need 100mm internal diameter, which sounds like soil pipe, and I've read an idea about cutting celotex disks to fit into the pipe at intervals and filling the gaps with broken celotex, but that sounds pretty bodgey. Is there a proper product for this?

Thank you!