You can buy adaptors to go from solvent weld to push fit.

Yes, thanks. Just found them in the Screwfix catalogue. As I've bought the
pipe and joints I think this is the way I will go.
It seems so fundamental that the two types are different, it just seems odd
that they are both given the same diameters! I done plenty of plumbing with
push fit in the past, I can't understand why I've never found this problem
before.