In article , TheScullster
writes
I intend to remove the blue/grey stuff which is very localised (about 1 sq
metre) and looks the most unhealthy.

I've been digging out a lot of the "pot clay" (yellow in our case) which
someone kindly dumped under our drawing room floor (don't ask!). It has
been dug up with a bricklayers trowel (not much room down there) and has
therefore come out in thin strips. I left these in a tub by a radiator
to dry, and found that they mix much more easily with compost in this
state than in big clumps. You can also put these dried pieces on a
concrete slab and run over them with a roller and reduce them to dust,
which can then be sprinkled over sandier parts of the garden (or you
could sew bags into your trouser legs and deposit it around the town).

John
--
John Rouse