Thanks for all your help guys.
It’s both dumpers mate, but I’d probably be starting on the smaller forward tipping dumper (with no roof). The rail do give you a full hi-vis waterproof uniform though and a hard hat (to keep the rain off 
), but yea…working in frost and rain laying kerbs / steels. The dumper tickets don’t expire though, only the cscs card does which is easy enough to renew after 5 years (it’s just a 50 question health and safety test).
The guaranteed job on the rail is what’s tempting me… but as you say I’ve got 2 years to pass the hgv practicals so no massive pressure. Maybe working on the rail as a dumper driver might look good on my cv when I start to go for new pass class 2 work? Not sure if employers see it that way? The rear tipping dumper (2nd pic) is massive, it’s like a class 2 hgv, so it might help.
Thanks guys