A quick update on my warrantied Ragley Ti frame mentioned above. Since I made the original post, I've been in discussion with Lynskey and they've very reasonably agreed to sort things out for me. I won't go into the details, but basically I'm happy with the arrangement and it's kind of restored my faith in the brand.
The whole warranty process was a little confused - essentially the warranty is through Hotlines, though the work is obviously by Lynskey - and all I'd say to anyone in a similar scenario with a cracked Ragley Ti is that it's worth getting clarification in advance on what's likely to happen to your frame.
There's a thread elsewhere on here asking whether people have every owned a bike that's perfect for them, I'll put my hand up and say that the Lynskey-made Ragley Ti does it for me and hopefully, thanks to Lynskey, it'll be doing it again in the near future.