Bill wrote:
In message , Tim Lamb
writes
Presumably the armouring will have been connected to whatever
junction box was used at the original load end by the securing gland.

If such a junction box were metal, it should give a good earth
connection..... I think you need some current flowing at 50HZ to
energize a cable finder.

Just some notes on this and earlier comments...

At least one of the boxes will need replacing, and there are visible
problems with one of the securing glands. I believe all the armouring
is still earthed though.
The main armoured cables are definitely coded red, blue, white and one
box has 2 whites earthed to the box. The third white in the same box
is tested live.
There is a bit of a family dispute (long distance at the moment)
about what to do next. I think we need to disconnect and measure until
we understand exactly what each individual wire does and which
direction the power goes. Son thinks we just have to find a way to
trace the cable until we find the underground junction box that he
thinks must be there.

Anyway, I have invested a small amount in a pre-loved metal detector
on ebay and will practise with it before he arrives back at the
weekend. I don't really expect it to work. It may have to detect cable
under crazy paving.

Running a new armoured cable on the surface tucked in at the base of
walls would be possible, but the amount of gardening work involved is
daunting and a couple of paths would have to be crossed.

I think I'd try measuring the cable capacity and resistance with a
DVM. Mine works down to about 10pF. By measuring each cable
individually, a break may show as reduced capacity, then measuring all
cables together relative to the shield will provide another guide.
Obviously the earth may be connected to the shield somewhere, so maybe
that's the point to go for a resistance measurement for the return path.
Looks like a very long pair of test leads are going to be required!