Thanks Milk and Speakno for understanding that this brave new world I am suggesting is not so impossible to imagine.
Lass - how many more ways can I explain this in this thread? I'll paint the scene this time.
Mother embarks on her return journey home. Takes expressed milk out of fridge or freezer. Places in cool bag along with frozen ice blocks. Heads to airport.
At check in/bag drop mother says ' I have a cool bag of expressed milk here, I believe I can pop it in the hold free of charge as it's too much to take through as hand luggage?'
Airline representative says 'sure madam, do you mind just unzipping it for me so I can see it is milk inside that cool bag?'
Mother - 'sure'
Airline representative - 'everything seems to be in order here, have a nice flight.'
NOTE: currently milk travelling in hold is not tested at this point, nor is it tested before it gets on the plane presumably unless airport security have worried about the bag. No change to this current situation proposed.
Mother then goes for a coffee (or potentially a bottle of straight vodka if she has been attempting to put forward a feminist suggestion to make working breastfeeding mothers lives a little easier on the mumsnet feminist chat board).
Plane takes off, milk stays in hold which is cold, plane lands. Mother picks up cool bag from carousel assessing how long the gap has been between plane landing and carousel pick up, checks whether milk is still cold/frozen and depending on what state it was in when she handed it in at check in, makes assessment on whether it is safe to put it in the fridge or freezer based on this, heads home, cuddles baby.
Showme + Cushion - This has already got far more personal to my own situation than I wanted it to, so I'm not going to get bullied into discussing my own child's medical condition or eating habits as it's irrelevant to my argument. However I will point out that given that airlines agree that breastmilk is an essential for a baby when the baby is travelling and thus will give it special conditions to be carried in greater volumes through security, is it such a leap to imagine that the same child needs the same milk when the mother has been travelling without the child, therefore that particular milk an essential medical item for that particular child, thus why should the airline profit from the mother being forced to pay a premium to carry that milk home?