This is what I thought. Unfortunately we don't seem to have any public weigh bridges in the entire county so will have to see if a local quarry will let me use theirs!
Somewhere on the paper work from your last plating there should be a figure of what your lorry weighs, but when I had mine weighed at a local scrap metal yard, it came in a lot lighter than the VOSA weight, so not sure how accurate the VOSA one is!
Out of interest, what does yours say, if you've managed to find it ann-jen? Mine was around 6.4t, but on the weigh bridge mine came in at just under 5.8, and although I had taken some stuff out it was nowhere near half a tonne!