yes it's all fine that as long as you don't load it to the max and stay under your vehicles limit it should be fine BUT
If say you have an accident and the van is totaled and spread all over the side of the road making it impossible to weigh it, I bet the insurance company will simply look at the plate and use those figures regardless of what you actually had in the van. So if the plate is higher than the limit of your vehicle then you are buggered before you even begin to argue with them. Just my 2c worth.
Sorry gypsy but that's not what will happen. The onus is on them to prove that not only you were overloaded BUT that it was the cause of the accident. The reply from transport is correct. It's how's it been with car trailers for years.