Until recently I had an area at the back of my garden which used to be
a patio but which I would prefer to be vegetables. So I have duly
removed the concrete and hardcore and am now left with a compacted
clay subsoil which I want to get back to life.

This is a serious clay so it it very compacted and very effective at
getting waterlogged but from what I have read clay although hard to
work should be fertile. So far I have double dug the ground and added
sharp sand (about 50 - 100 Kg / sq.m) and composted manure (about 200
l / sq.m). What else should I do to get this to something that I can
grow on

JB