James wrote
James said
ARWadsworth wrote

A photo from outside might give more clues.

Not much to see out there at the moment, but I'll take one when it's
light.

Ok -- here's a couple more pictures of outside:

http://tinypic.com/r/kef4gi/6

http://tinypic.com/r/29zzlvs/6

It's noticeable that there's no rust on the pipework, which I suppose may
suggest it's not cast iron.

Nope, cast iron railings don't rust.

Look at the top section of the second picture where the paint has come of.
It doesn't look like metal to me, at least from a distance.

But where the white plastic pipes clamp on
in the first one doesn't look like a clay pipe
as far as doing the hole is concerned.

Cant you just tap it gently with a screw driver etc ?

Next door's soil stack is identical but has lost a lot more paint, and
that hasn't rusted either.

The white plastic pipe is coming from a Saniflo at the front of the house
and will be removed when I do the bathroom.

Then you will be able to see if its cast iron or clay.