I was in my local Asda today (Robroyston, Glasgow) where they are selling sharesize 1.25l bottles of Coke or Diet Coke for 2 bottles for £1.00. It is normally £1.23 for 1 bottle so this is a good deal. Not sure if this is just Scotland or nationwide. I checked online but it shows up as £1.50 for 2 on there.
I have stocked up for the summer and bought 40 bottles so that should last a few weeks.