Bloody hell! I finished my last edit of the new book last Thursday, e-mailed it to my agent on Friday, and got an offer on it today. Just shows what publishers can do if they want to.
Another bit of good news came with the offer. The last book - "Other Countries" - earned out its advance in the first eight months, with other revenue streams still to open up.
I'm glad I didn't retire fifteen months ago, after all!