The 18th edition regs have a complete section on wiring in caravans and mobile homes and double pole circuit breakers and 2.5 mm wiring are a requirement as you say and even caravan manufacturers don't fit them as they don't know the regs but the latest edition of the regs now state that if someone is injured due to incorrect wiring the HSE can prosecute and if your van catches fire due to a wiring fault you might find you're not insured
Been reading through this thread with interest as just the other day I needed to do a bit of work on my mains system to wire in a new inlet and on board battery charger. I originally fitted my consumer unit 20+ years ago and having read the above, hastily dashed out to check exactly what I did fit all those years ago. It looks ok to me but really I only borderline know what I'm doing . So does my set-up look to be compliant or is it time for an upgrade?
the regs are not retrospective so it looks fine but if you where to change it it would need to be to the current regs