(This is all thanks to kellyh at hotukdeals)
Gap at the moment have 30% off jumpers online. The website applies that automatically. BUT they also have a promotion where if you use GAPSAVE30 you get another 30% off, plus if you sign up for emails then you get a further 15% off (you need to click the link via the website and they send you a personalised code). It means that for anything you buy you get 40% off, but jumpers works out at nearly 60% off.
Included in the jumper sale are all their cashmere ones (which they don't usually have in these sorts of deals) - I just got my sister a fab one for Christmas.
(You do need to pay £4 postage but it is still a bargain).