Right! All stripped down to a bare frame now.
It would seem that cream is the original colour, as the paint on the steerer tube is perfect condition.
To answer a couple of questions, the chain stays are indeed 16 1/4", the bottom bracket shell is 68mm and has English threads and the seatpost is 27.2mm.
Looking inside the frame and at the lugs, it is apparent that this is a pretty well made frame, but definitely a 'cooking' model as Shaun suggested in the first place.
I now have to decide whether I get a local paint shop to strip and respray, or whether to take the frame to a builder and have a few of the rougher edges taken off before having it sprayed.
One slight worry is that the bottom headset shell is a loose fit and dropped out with the forks. I looked for cracks but can't find anything untoward, so I'll probably reinstall it with a bit of loctite.
I'm currently negotiating a few more bits from the previous owner and watching a few more on the bay, so this build is actually moving much faster that I first intended.
I'll take some more photo's later and I'll start a new thread in the riders bikes section once a few of the bits turn up.
Aren't old bikes interesting.
"Try not to punch any clowns"