Not sure if national or not, but I've just bought Oblivion on the PS3 for £9.99 in my local Gamestation (Stockton-on-Tees). There was a shelf full of them there, too.
The guys behind the counter said that Head Office had ordered too many, so they were selling them off, so I'm guessing it's a National deal?
Just looked on the Gamestation website, and it's still £34.99 on there, so must be instore only...
It's an excellent game (albeit a little old now) - highly recommended, definitely worth a tenner!
Here's my receipt, in case anywhere will price match based on this:http://i219.photobucket.com/albums/cc320/hodsey77/P3210120.jpg
Here's the actual photo of the game, with the discount sticker on:http://i219.photobucket.com/albums/cc320/hodsey77/P3210122.jpg