Similar to the ones you'll find on DealExtreme for around $5 (and on eBay for around £4). 'Gamexpert' branded (part number GS-781), and IMHO much better quality than the ones I've bought from both DX and eBay. Comes with a carabiner style belt-clip, and the zipper moves very smoothly (unlike the other ones I've bought).
Blurb from the back of the packaging:
* Hard case to protect UMD
* EVA shock absorbent construction
* Holds 5 games
* Store up to 2 memory cards
* Carrying hanging hook
They had plenty of these in stock in my local branch (Hamilton), and I'm assuming that they'll be available in other branches across the UK. I only saw black ones, so I don't know if other colours will be available.