FWIW I've been pondering whether or not to take my B+E for the last couple of years.
The thing is, whether the rig is technically cat B legal or not, by the time you've been pulled, explained that 'no officer, it IS legal because blah blah blah', (because the authorities DON'T always know the details inside out) had the police / ministry crawl over everything looking for plates and possibly dragged you off to a weigh bridge to prove yourself, you've already lost your day out.
Better to be safe than sorry and if in doubt get the B+E as you have done Johnny. Besides that, then you don't have to worry when replacing your car / boat as you're already covered.
Either that or live with someone who has a C+E...