Thanks - as I said to Nick, the idea is raised beds on top of the sand and
soil, with all that you mention incorporated below a layer of topsoil,
with an eye to the long plan. In the first year I imagine each veg they
manage will cost an eye-watering amount ...



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Klara, Gatwick basin

If the clay is that bad you cannot grow in it ,maybe you would be better off
digging the clay over,put deep raised beds over and fill with a good top
soil,then every year put a thick mulch on top and let it work in before you
start planting.The other option is to go for it on improving your clay with
organic matter,ie compost,manure and grit.Sharp sand maybe to fine be
careful what sand you buy if you go for the sand option.One thing you did
not mention was the size of plot we are talking about?
Cheers Keith
Nottingham

The clay isn't solid, it would probably be possible to dig it and plant
in it, but they want to start improving it as much as possible straight
away. The whole eventual area must be about 5m x 15m, but they are
planning to start with just two raised beds maybe 1m x 3m and gradually
work their way over the garden. (Like everybody else, work and commute
takes too many hours, so it's weekends only.)

Are we overestimating the quantity of sand they need at this stage?

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Klara, Gatwick basin