One for £1, two for £3

Odd supermarket offers: a packet of biscuits costs £1, and two packets cost £3

The big white £3 on the red background suggests this it is a good deal, because you get two of the product for that price. However, it is a little odd in this case, since if I buy a packet of biscuits, it costs £1, but if I buy 2 packets, they cost £3. The prices are also helpfully given per 100g: buying one packet at a pound costs 55.6p but buying two packets at £3 equals 83.4p. The branch of the Co-op nearest to where I live has form in this kind of odd offers (see One for £2, two for £5). I have to wonder who makes the decision for these pricings and offers. Are they determined at the Co-op HQ? Regionally? Or are they up to the manager of the shop? Surely someone in the organization must realize that this does not really make sense? I was tempted to buy a packet of these biscuits, just one packet, but somehow managed to resist.