Hi, again, all--
OK, here's the scoop: Demand for this book has exceeded supply. The book channel in particular has had unforeseen levels of demand. Amazon.uk may well be out of the PHB2 (we don't have point of sale data on it yet, so I can't confirm that); if that's the case, it will likely be several weeks before they have more.
Your best bet is your FLGS. As has been pointed out, the UK isn't exactly crawling with FLGSs, but there are over 100 sites in the UK, outside of the book trade, that carry D&D. Check out
www.findyourgamestore.co.uk if you're looking for an FLGS. If that doesn't work for you, most Waterstones should be able to help you out.
Hope that helps!