I went into sainsburys last week, and i bought groceries coming to £3.92, and i got a voucher. Which says
Valid from 14/3/2011 - 12/4/2011
£3 off when you spend £12 on Tu clothing.
I didnt buy any clothes to get this, so i assume it comes out the till when you spend money. not sure if this is just selected for me, as i dont really shop there often, maybe once a month..