being a farmer/farmer's son myself i can say categorically that i thankfully know of no dairy farms within a pretty huge radius of ours where the cows don't live outside for the most part. they bring them into the sheds at times but only when there isnt grass (snow) and to protect them from the extreme weather in the winter on the whole.
reasoning being, cows fed on green grass, not only produce the best quality milk but also the largest quantity milk. this makes it cheaper and easier for the farmer to make more money and have healthier stock, which, for any real farmer, matters more to them than a lot of people realise.
whether im in lincolnshire or leeds, i would have to physically seek out milk that wasnt from outdoor cows. perhaps that's just another good thing about living in the rural north and since it costs so much to transport liquids, you can always be sure that supermarkets stock local milk from local dairies
talking of student budgets, i know just what you mean. I only buy free range eggs, but then i feel there only should be free range eggs, and i only buy british where i can. no danish bacon for me haha, and a plea to everyone, when you're buying meat, or in fact any produce, look for the little red tractor symbol. british grown, british farmed, british assured. if the consumer doesnt support the british farmer, who will?? certainly not our government!