Right everyone. Apologies for my online absense - I didn't really feel like I was making any progress.... until a few days ago.... And I've since been very distracted. And I think, with a kind of tremulous excitement, that I might have found something. I have been all over literary London - the British museum, Doughtey Street, the London Library, the British Library, the Sherlock Holmes museum, you get the idea - and I just hope my peregrinations have been worth it. If not, I'll be quite embarrassed. And back to square one. Now I just have to wait and see.

Thanks to all those who have been in touch. And if my half-baked unlikely theory has some substance, then I'll let you know...