I forwarded these links to my friend:
http://cgi.ebay.com/ws/eBayISAPI.dll...ayphotohosting
and
http://www.sheldonbrown.com/retroral...ofessional.jpg

He reckons it's a good match except the Professional didn't have cable guides and had different seat stay eyes and rear brake bridge. He also says there's no sign of there ever having been a head badge riveted on.

I've written to him saying, "Is it possible that the paint was not original when you got the frame? If it wasn't perhaps the cable guides were added, the seat stay eyes filed and the headbadge holes filled at a re-paint. How is the bridge different?"