Staying with families was actually a kind of an insight in "real" life in Britain. That´s why I always tried to find such a trip. Yes, these travel agencies cooperate with certified groups of families almost in every town. There is a coordinator who distributes the tourists, of course they see to the needs and wishes of the clients.Or at least they try.
But it is also always a big adventure because you never know what kind of people you are staying with - and sometimes it is a surprise, especially for those who experience this for the first time of those you expect luxury.
I managed to stay with lots of people in England, Scotland and Wales and I always was lucky to meet nice people and only once the family were indifferent and took us tourist like a difficult insects (but still provided what they were supposed to).