Noticed this deal at Boots in Hammersmith today whilst getting my (last) O2 Priority £1 meal. Didn't need a USB but bought this cos it was so cheap. Seems to cost £12.99 at Argos and £6.99 at Currys. Not sure if other stores have this discount, but cashier scanned the barcode on the back of pack (rather than the clearance barcode) and it discounted this item anyway.
*instore deal - See link for specs only