Because it was made in association with HBO, it's very unlikely that it'll be released outside the UK (perhaps some European countries as well; I'm not sure if they're in the same Region format). They were told something along the lines of "HBO makes their money from their Pay TV channels, and have no interest in home video releases". This is, of course, after the North American film distributor they were working with went bankrupt. So as far as I know, it was in theatres for a while, got a UK DVD release, and everybody else has to hope they catch it on HBO when it's sporadically aired.

However, awesome movie. I'm mulling over doing a review of it here, which is how I found your post.