Apparently I need a tonnage survey. This consists of a man with a tape measure, a set of tables, a nice red seal, 5-10 minutes of his time and a bill to me of about £1500.00 Nice work if you can get it.
I had to do this also but luckily it only cost me about £250 (I think) and was arranged by Shoesmith's the legal eagles that Lombard put me onto as part of the registration/mortgage/purchase process - I expect your GB will cost rather to process more than my 31' Nimbus did!