Do I need planning permission?

Usually not. Most garden rooms are permitted development, provided the building is single storey, sits behind the front wall of the house, covers no more than half the land around the original house, and stays inside the height limits. Conservation areas, listed buildings and flats are treated differently. One local point worth knowing: parts of south Bedfordshire around Dunstable, Whipsnade and Totternhoe sit inside the Chilterns National Landscape, where an outbuilding more than 20 metres from the house is capped at 10 square metres before permission is needed. Twenty metres is not far down a long garden.