We did have an announcement here recently, based on the book's listings on Amazon (USA) and in Publishers Weekly. But, your post adds some new and different info.
The US Amazon site shows it as supposedly released on July 28, while Editor & Publisher now shows it for September.
Since neither Amazon nor the publisher's site shows an image for the cover, we may find the US release is later than Amazon now states. But, Peter's book seems to clearly be in the pipeline, and I'm glad to get your report that it is coming to the UK.
Update and correction: The publisher's web site now shows a cover image (and still shows the release date as "Fall 2006").
It's a close-up of Peter Falk, definitely as Columbo, with cigar and raincoat, looking shrewd and suspicious. It reminds me of a black-and-white head shot of Columbo that a lot of you have seen, but this one's in color.