None of the Tesco or Morrisons stores near us seem to stock the deals for Box Office Smash (BOS) at £15 but Toys R Us are selling the previous game - Lights Camera Action (LCA) - with the buzzers (which are identical to those found in BOS) for £9.99 down from a marked price of £19.99. Had a few on the shelf at the Parkhead Forge store when we were in earlier.
LCA and BOS are fairly similar but if you want the latest game and can't find it cheap with the buzzers, pick up a copy of LCA with buzzers at Toys R Us then grab a copy of BOS solus for at most £10 (from Amazon for instance but worth checking on HUKD obviously first!) This is an instore deal only - not showing online at all
EDIT 2: For anyone struggling to find a copy at Toys R Us, Zavvi have it for £12.95 delivered and showing stock (as of 24/7/09)