This deal is done via Currys price-match policy (as PC Worlds is the same it will work there too).
HMV are selling DJ Hero for £49.99 (I bought Xbox 360 version but same goes for PS3) and Currys are currently at £89.99, so Currys will do a price match with an extra 10%. The branch I used didn't want to mess about with the pennies so did it for a straight £45! Bargain.
(My first deal so sorry if I've done anything worng)