I know this is probably not nationwide but is more of a heads up for anyone who is looking for this locally.
ASDA living at Cortonwood Barnsley have about 4-5 copies of Guitar Hero World Tour (game and guitar) on both systems. Priced at £35 for PS3 and £39 for Xbox 360.
i was lucky enough to get one from comet for £29.99 and I've heard HMV had this cheap but I haven't seen any locally so this is a decent price (better than any online).
May be nationwide, the games were just in single cases, displayed with the other games.
Guitar Hero World Tour game only was also £10 for the 360.