May it have been built by Bill Grey? He was very adept at lugless builds like my Dave Russell (note- -lugless BB as well) and was active in the London area in the time period of this frame. I think the OP's framer is lovely - but it's to small for me!
I don't know if there is any evidence to suggest that Bill Grey ever built lugless frames for Shorter, whereas Barry Chick certainly did. Thanks for posting this though, the brazing on the head tubes looks very similar indeed to mine, though you'll probably agree that the bottom bracket doesn't seem quite as elegant, not least because of the brazed on fittings.
What's the rest of the frame like, I'd love to see some more photos..