Thanks for the tip. I went with this in the end. 179 Litre Euro Stacking Container (800 x 600 x 450 mm) from Totebox. Want to be able to ferry as much shit as possible from one place to the other in one trip, will have to do it multiple times.
Nice one, Kev - sorry I missed the earlier questions. But yeah, long time ago now but pretty sure that's exactly the one I used to have. Hope it proves as effective for you!
If you want semi-permanence, there's also the tough stacking crate and ratchet strap option:
https://www.utzgroup.co.uk/stacking-container-800-600-325/