Victor seat cluster was a Shot in design and not a fastback, that's how I read it.http://www.carltoncycles.me.uk/mybikes/66giro.htm
The fastback frame with horizontal dropouts is a bit of a mix for the OP's frame as track frames usually had widely spaced seat stays at the seat cluster for maximum strength........ all in all an unusual mix of features.
having typed the above found a track frame on Hilary Stone with fastback..typical LOLhttp://hilarystone.com/images/sale%20im ... s-2000.jpg
One argument against the USA Carlton/Raleigh connection is the likelihood of the frame crossing the 'pond' twice?...more likely is AB or someone other bought a set and incorporated into this frame.
It is interesting that the owner of the frame descibed it as 531c.....but if you notice the 2008 pic there was no 531 decal...so either word of mouth or inaccuracy.....AB did make frames in the 1960s and likely after Carlton closed in 1981.
Shaun....from a cryptic Zeus 2000 mention in the HS link...i found it on his website....same time frame as mine being 1970s-1980s and 531 double butted.
The Carlton link has the T in the frame number which mine does not.