In uk.d-i-y, Charlie wrote:

....................................... do I try and pull a new cable
thru the existing boxing which also contains the pipework?
.................................. Will the new cable be up to being
pulled through about 15metres of boxing, 2 walls and 3 corners.

No to both questions, I'm afraid! For the first, it's not accepted
practice to run mains-carrying cable in the same compartment as
pipework, on grounds both of heat (presumably the pipework includes
the boiler output - 70-80 degrees?) and of what-happens-if-there's-a-
fault-exposing-conductors (like, we're pretty sure the pipework's
earthed, but just *how* sure are we?)

For the second, pulling cable round three corners, expecially with
other pipework in their, is pretty much doomed to failure; and likely
even if you manage to damage the insulation.

But hey, maybe you can use this as an excuse to buy a nice new SDS drill
so you can channel the 4-core neatly ;-)

Stefek