hotels and B&Bs must have 4 cartons of UHT milk on each room's hospitality tray. it's a rule. this is regardless of the number of people staying in the room, the size of the cups, the number of teabags and coffee sachets, or even the price/poshness/star rating of the hotel.
no more and no less.
i have only seen this regulation breached twice: the occasion of less milk appeared to be a rushed-room change, the occasion of more milk just seemed like a flagrant disregard :)