Why can't I have my whole family in one room?

In the UK landlords rent individual rooms to individuals or occasionally couples. It is not culturally acceptable for a family to share one room.

About our accommodation: What types of accommodation do you have?; What is provided in the rooms/houses?; How can I buy household essentials?; For whom are individual rooms suitable?; What do I need to know about rooms?; Why can't I have my whole family in one room?; I want to do a house swap. Can you help?; Will I be able to eat in college?