Ade wrote:
I have a new allotment with new raised beds, on clay soil. I want to add
soil or compost to the raised beds. It's a new allotment so I don't have
any home-made compost, so I'll have to buy some.

What's best to use - B&Q multi-purpose, fancy soil conditioner, ordinary
topsoil, or something else?

Well, not topsoil for a start!

Assuming a four-bed rotation, add B&Q cheap soil conditioner and manure
to the potato and brassica beds, soil conditioner alone to the legumes
and nothing or soil conditioner alone to the onion/beetroot etc. bed.
Only one spadeful per square yard is needed. Clay soil is very
nutritious: what is needed is organic matter. Sharp sand/grit can also
be dug in to improve structure.