What is the difference between the supermarket Longlife value skimmed milk that costs 49p, and the more expensive "standard" skimmed milk costing around 20p more?
Can I suggest cravendale instead. It has a very long shelf life anyway (compared to ordinary milk) and it can be frozen if you need to - bottle expands a bit, but no problem.
It also keeps longer once opened. I live alone and one bottle can last a week, but it still tastes fresh.