does anyone know of any decent property auction companies?
primarily residential, but with a view to developing (esp unusual properties)
Allsop have a fair amount - not sure about unusual properties though
I’ve bought from Savills & Barnard Marcus before now. Nice and easy.
Need any advice, gimme a shout. 
winkworth
GANE NEWs - rare and cheap normally
Can’t add anything worthwhile to the list of companies, there are simply too many. Best go on line and start making your own list.
As for rare/interesting/unusual properties, just about all of them will have them from time to time if there is money in it for them. A good few years back I went to bid (for a developer) on a load of tiny East Anglian village telephone exchanges being sold off by BT. The same auction also had a light house and what remained of an Irish castle.
All these and more were sandwiched in amongst commercial buildings, commercial rent packages, whole streets in northern towns and domestic property between £20 odd K (Colne, Lancashire) and £2 mill. (Guernsey).
If my memory serves me, I think that was a Saville’s auction.
is your need as a vendor or a purchasor, 2 very different agendas, feel free to P.M. me as it is my trade and has been for over 20 years.