On 04/08/2018 16:06, GB wrote:
I've got the wheel and caliper off, but I apparently need a brake
caliper rewind tool - on order, and I'll collect it tomorrow.

Can folks please confirm that I can't just push the caliper back with a
G clamp?

I have seen a youtube video of someone doing that on an Astra H
rear caliper. The trick is to apply pressure with a clamp and
at the same time rotate the piston.

Some cars need a pair of rewind tools becuse each side is
handed.