but if you use T&E, put it into alkathene (blue plastic water main) it's
unlikely to come to any harm, especially if you place bricks along any
lengths that are likely to be dug into.

The colours of underground services are an important safety indication and
should be followed. Blue MDPE water pipe is not acceptable as a duct for LV
electrical cabling. Quite frankly using anything other than SWA cable for
this application would be silly.

Some of the colours, I'm sure there are more I've forgotten:

Blue = Water
Yellow = Gas
Red = High Tension Electric
Black = Low Tension Electric
Grey = Telecomms
Green = Fibre Optic
Orange = Railway Signalling
Purple = Motorway Signalling + Power

Christian.