I didnt? is that the case? It would be easy to state that any road is 30 unless otherwise stated which -is- actually the case, but dual carriageways tend to always be 40+ in my experience.

At a rough guess I would place it as 2x a single carriageway? normally in areas where there are less/no immediate houses and hence the reason they can put 2 lanes in and go faster than a 30 road the dual carriageway running through my town is 40, the one running at the side of the town is 70, and the only one I've come across that I know is 30 is the one I got caught on. Maybe in Poole things are different.