This is the cheapest offer I have come across. Note these are the big 1 kg boxes (not the 500g boxes that have been recently posted), priced at £2 each (which is fantastic anyway) or buy 2 for £3.
I think this promotion started today as staff weren't even aware of it.
Just checked offer is not online - they have the 500g box on 2 for £3. Worth checking your local Asda during your next shopping visit.