I went into Tesco today and they are advertising 25% off all of the mens, ladies & kids nightwear. It includes all the slippers, dressing gowns, pyjamas and nighties etc.. so some really good savings.
TIP- They had lots of twin packs of girls pyjamas (all ages) all price marked at £7. They are lilac/pale blue with 'I'm a star' written on the front of one top, and the other with just stars. The bottoms are one pair stripey and the other with stars also. They are scanning at £5 and then take the 25% off making them £3.75 for two pairs! - so it may be worth checking in other stores for the same :)