Thanks for the advice.

Having obtained a couple of transition MDPE adaptors from BES and a short
roll of 25mm MDPE from B&Q, all is clear.

Turns out I'm not jointing to copper underground...

We dug the hole out today. 1 yard down, 2.5ft x 2.5ft. Could we find the
pipe - buggery we could...

Dug (well undermined) the side of the hole and found one rusty iron pipe
(prob old water) and one black electricity cable at 0.4m depth (so I
thought - read on)...

So we dug next to where blue copper pipe comes up (1 yard further down the
path). Found it there - 400mm down. Dig a bit more, and found a brass joint
in self amalgamating tape, where the short bit of newish copper changed to
some black plastic stuff...

Back to the "electricity cable" - quick diameter measurement with vernier
doobrey confirmed that muddy black thing was in fact the water pipe, not
the cable.

OK - good. We have pipe in the correct new hole. A call to SE Water's
technical dept suggested the pipe was probably 1/2" black polyethylene
(PE). Good, my MDPE transitional adaptor does PE.

----

Managed to core drill (66mm) a very neat hole down through the floor inside
the house, and with a bit of help from a 1m SDS drill, and more core
cutting, we got through the strip foundation and into a small hole we'd
burrowed under the foundation, from the bloody big hole outside. Result...

I should add that in the older part of the house, our strip foundation
concrete starts 2" below ground and stops about 8" underground. It sits on
earth, not clay.

Apparantly my house should have fallen down years ago...

Anyway, we can easily get a 110 rest bend under the house and I plan to pop
a bit of 50mm waste pipe down from above to form a sealed duct into the 110
and add a bit of extra 110 pipe on the outside into a little brick
inspection pit and dump the joint in that. Makes it easy to re-lay the pipe
from the house in future...

Photos will come...

Cheers

Tim