I've been mulling over a powered trailer DIY project for picking up decent sized loads of wood, but when idly checking the pricing on a proper Carla powered trailer(yowza, DIY for sure) I found one retailer claiming it's illegal to use a powered trailer with an ebike as under UK law despite both being legal 250w motors it counts as being combined into a single 500w one once you hitch one to the other, which seems extraordinarily dumb, but not so dumb I'd put it past our lawmakers.
Is that actually correct, because they don't specify a source and a casual google hasn't turned anything up, but you'd assume they're not deliberately sabotaging their own business needlessly...