Morrisons are currently running a promotion for "3 cans of Batchelors condensed soup for £1". Flavours are mushroom, tomato and chicken and includes the low-fat variety. The price of these varies from 41p to 44p.
However, there's a misprice on the till. For every 6 tins you buy, the till deducts £1.12. Therefore you can get 6 tins of the 41p variety for (6 x 41p) - £1.12 = £1.34 = 22p per can.
This mistake was in effect yesterday and I've just been back to stock up and it's still happening.