One or more garden sheds or summer houses may be erected within the curtilage of a dwelling provided the cumulative area of ground covered does NOT EXCEED 15sqm, the height must be less than 2.8 metres above ground level and the shed/summer house cannot be placed between the dwellinghouse and the highway, other than where it can be placed more than 20 metres from such highway.

ALSO the generic conditions can be met, Part 2, Section A (Page 15) and of the Permitted Development Order.