I think it is from an AL8 track lamp e.g. Tilley AL8 1950 - 1954 This is where the frame attaches to the tank.
Great find! Wouldn't be too hard to fabricate your own frame for one of these either? There are more pics in the gallery of very similar ones like yours = www.classicpressurelamps.com/forum/showtopic.php?tid/1104/post/new/#NEW The little hood/galleries arrangements are scarce, but they do come up now and then? I think they are the CH1 conversion head? p
There's two lamps similar to that apparently used by B R on gumtree in various states of repair, nothing to do with me, if they weren't so far away i'd be going to have a look although i wouldn't know what they were worth.
Too far for me with that price ...what we need is someone in an old sports car pretending to be off 'Antiques Road Trip' to go and blag the price right down! ...Who's nearest to Scarborough???