Hi Mans,
Not sure whether to post this, as I don't want it to sound like a terse reply. Here goes -
Is it lugged or brazed? Oversize or standard sizes? Have you been able to weigh it, to get a wieght for frame/ forks only - this could rule some steels out and narrow the search a little.
Easiest option - Is there a frame number? If so, you could ask Roberts direct of they still have any info.
Good luck,
David