how much cement/gravel/sand to make up 1 cubic metre please?

2.3 tonnes, typically 4parts gravel/stone, 2 parts sand, 1 part cement

It depends what you are using it for; a typical mix for foundations and ground slab might be 1 part cement to 8 parts all-in ballast - ballast is a premix of large [up to 40mm] and fine aggregate [sharp sand] in the ratio of about 6 to 2 and should not be less than 100mm thick for slabs. As a base under a shed in the garden for instance, you could use a 1:12 cement/ballast mix.

Is there a reason for not using all-in ballast? If not ask your supplier for 1.5 ton all-in (this is a ready mixed aggregates, suitable for most types of concreting. And you'll need about 8 bags of cement (o.p.c(ordinary portland cement)). The mix you need depends on what you are doing but head around 6 parts ballast to 1 part cement.

A cubic meter is 1 meter long by 1 meter wide by 1 meter high (or 3.28 feet long by 3.28 feet wide by 3.28 feet high)