Saw this in Morrisons but guess it will be in other shops too.
Gaymers Pear Cider with Berry fruit, botles have a collar around the neck with a token on to send off with your receipt and a leaflet printed off from here : http://www.gaymersfruit.co.uk/
to get a refund of the purchase plus postage.
Its £1.67 a bottle but part of a 4 for £5.50 deal so you will actually get back more than you pay if you buy 4.
EDIT . PLEASE note under site rules this is not actually a freebie. You have to buy the item and pay postage ... you get both back but that doesn't count under the 2009 (amended) freebie act. I'm really sorry for misleading people.