There are Cheerios and about 4 others cereals (Nestle ones I presume) on the 2 for £4 deal.
They were selling at £2.67 per packet.
Two packs should be £4, but they charged £5.34 and then took off £1.98
Which means both packs cost £3.36.
It looks like they took 99p of each pack!
Not ground breaking I know, but I think I would have bought more, had I have known.
Hope this helps someone!