Tesco instore at Toton are selling their own organic 100g chocolate bars for 39p. They have then been marked down further to 31p. I think the original price was 78p.
Its a good quality bar with 40% cocoa solids which is high for milk chocolate. The use by date is Nov 2009.
Judging by the label I assume the 39p offer is nationwide, however the 31p offer may be store specific. Couldn't find online I'm afraid