Regulations for burying wires etc

I have looked on the Wiki and searched the threads but not found anything recent.
A friend of mine has built a large room/big summer house (all within planning regs etc) at the bottom of his garden (10-15m from house) He intends to have power, coax and network run to the building. He wishes to do the donkey work himself to keep the electrician costs down. I was thinking 2 PVC pipes (1 for power and 1 for AV/Data) stick a draw wire and then he/electrician can pull the wires when needed.
Questions.
Is this acceptable? I know that SWA doesn't require a pipe but this would mean he doesn't have to leave an open trench while he gets the electrics done. Does the electrician have to see the trench construction as part of the sign off to comply?
How should the trench be constructed? Depth? sand or gravel in bottom? Tape indicating buried wire?

Thanks.

Digging a trench and putting in conduit with a draw wire is the only way, unless the elecrtrician is there to see the cable put in the trench and covered in.
here is a guide to depths, etc

Depths depend on what the surface is used for!

You must have separate duct for power and dta. leave at least 50mm between ducts.

Google CIVIL DUCTING for suitable products

Taylortwocities said:

Digging a trench and putting in conduit with a draw wire is the only way, unless the elecrtrician is there to see the cable put in the trench and covered in.

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Even then he'll want to see/be assured of the depth.

MARK - as ever, best thing is to get an electrician engaged before you do any work. If you really, really, really can't, take photos to show the depth.

Google CIVIL DUCTING for suitable products

Click to expand...

Or twinwall duct(ing)

Thanks for the replies. Most helpful.