What can I build ?
Previously you had to leave a one metre gap between your building and any garden boundary if the internal floor area of your studio exceeded 15 sq. metres. That is no longer the case
Provided your building is less than 2.5 m in overall height, then you can now go up to 50% of the area of all your garden. The area of your garden is all your land except the part the house stands on, so the area includes the front garden, side gardens and back garden, less the area of any other buildings, fuel tanks etc.
There is no change to the rule that no buildings are to go in front of the front elevation of the house
The 30 sq m max size rule, no longer applies either, the 50% rule replaces it so garden rooms, provided they are single storey, can now be a lot bigger, depending on your garden size.
If you are in a conservation area, then you cannot have anything at the front or side but now, no longer need permission to place a garden room in the back garden within a conservation area. Before you had to ask for permission wherever it was sited, if you were in a conservation area.
Studios within the garden of Listed buildings, you need full planning as before.
You must go for planning permission if it is being used for overnight accommodation whatever area you are in.
Within Areas of Outstanding Natural Beauty etc, the rules are the same as before, max size of 10sq metres at least 20 metres away from the house.