1 Contact the British Proof House's.
2 Name and shame ,there is no excuse for this sort of practice.
3 It is an offence under British Proof Law "To expose or offer for sale " a gun that is out of or unproofed. The offence is absolute and there no exceptions. As Lapogus Say's there is provision for a recognised dealer/repairer to take possession of barrel which have had a section cut away,for the purpose of sleeving.The only other way the gun may be sold is if a Proof exemption certificate is issued ,but this will onlt apply if the gun is of significant historical interest.
As to the rest auctioneers are there to sell for the best commision,some are not "reputable dealers" and still cling to the old adage of "buyer beware".
4 It is an offence to export a gun which is out of Proof or is unproofed.
Yes I have had some bad experience with them in the past,and so have many others.