Paul L, Please check this because I could be way off the mark, but I understand what you are saying is correct in normal circumstances if the sale goods have a commercial origin. My understanding is that if the sale item has originated from a private source or education then VAT is only payable on the buyers premium.
I am only stating this as I am located not too far from the auction house and, although over twenty years ago now, I used to go regularly to the sales and I bid for several machines and tooling there. To the best of my recollection I did not pay VAT on the hammer price for a Boxford shaper and a Harrison miller because they had originated in education, but VAT was levied on the buyers commission. I can recall paying VAT on the total net price for some tooling I bought out of industry.
I could be wrong and my memory is playing tricks on me, but that is my understanding until I am corrected. I am certain for anyone who is interested in bidding, a quick phone call to the auctioneers should clear up any mis-understanding.
Edited By Chris Crew on 02/07/2021 08:55:43