The Public Records Office say they hope to be back up "soon" and are just doing "final testing" -- but they don't have as firm date for relaunching the service.
Oops! Sorry about that. I'm used to Jeeves, which was HTML (and had a facility to edit one's boo-boos afterwards). Anyway, http://www.pro.gov.uk/about/access/statement.htm
is the page with the latest, straight from the horse's mouth.