Spotted in 2 stores (Stockport and Wythenshawe) while I was hunting down the £45 Sanyo camera. Games found within the relevant chart sections for each console with yellow shelf edge labels saying £25. NOT store specific and a markdown of games that have passed their sales peak or are underperforming anyway.
Recent release Fuel for £25 on both consoles, plus the following again on both for £25:
Call of Duty: World At War
Resident Evil 5
Street Fighter IV
Also, just for the XBox:
Star Ocean: The Last Hope
Sadly, this price didn't apply to Red Faction: Guerilla or Prototype, but maybe after a few weeks...