Thanks for all the suggestions. It was really simple, as it turned out: the long hoop of metal at the end fits over a captive bolt on the side of the car and is secured by a nut and washer. It's easily accessible as it's not underneath the bolster, but below it:
[url=http://s1372.photobucket.com/user/sfjwebcomms/media/Car/DSCN5683.jpg.html][img]http://i1372.photobucket.com/albums/ag349/sfjwebcomms/Car/DSCN5683.jpg[/img][/url]
[url=http://s1372.photobucket.com/user/sfjwebcomms/media/Car/DSCN5668.jpg.html][img]http://i1372.photobucket.com/albums/ag349/sfjwebcomms/Car/DSCN5668.jpg[/img][/url]
I must have missed it last night as it was getting dark. It's really obvious in daylight. I didn't have to remove any trim, it was in view once the back seat was out. Meanwhile the hook in the middle of the bolster keeps it in place by hooking over this plastic lip:
[url=http://s1372.photobucket.com/user/sfjwebcomms/media/Car/DSCN5682.jpg.html][img]http://i1372.photobucket.com/albums/ag349/sfjwebcomms/Car/DSCN5682.jpg[/img][/url]
I'll put up all today's photos later. I have the back seats & bolsters fitted but I'm ready to throw a large tantrum over the bolts holding in the front seats. I just can't get them loose. Sundance currently has a two-tone interior, cloth in the front, leather in the back
S
EDIT: was a 12mm spanner, as were all the bolts securing the folding back seats. The front seat securing bolts are 14.