I got formula for my twins last week at gatwick and i got ottles of fresh milk just by the gate at mco. I asked at check in if i could get some from the crew but they were ot sure if they would have enough so purchased some sma from boots to tide us over till we got to walmart
If I remember rightly the self service place sold cartons (to go with cereal). We asked at one of the coffee places and they were kind enough to fill my DDs drinking cup for free
There is also a Boots at Manchester but I don't know if they sell it.
You can buy it in WH Smiths at Manchester Airport once you are through security. We have travelled several times with babies/toddlers and know what it is like trying to get milk.