Two satellite dishes can be installed on a house without needing planning permission. They can be on the house itself, on an outbuilding or in the garden. One can be up to 60 cms in diameter and one up to a metre, provided each dish’s cubic capacity does not exceed 35 litres (the cubic capacity is the volume of the dish, i.e. if it were filled with water, what would be the volume of that water).
If the satellite dish is on a chimney, it should not exceed 60 cms in diameter and it should not project above the top of the chimney. If the satellite dish is installed on a roof without a chimney, it should not project above the highest part of the roof. If it is to be installed upon a roof with a chimney, it should not be higher than the highest part of the chimney or 60 cms above the highest part of the roof, whichever is the lower.
On Article 1(5) land, i.e. a National Park, an Area of Outstanding Natural Beauty, a Conservation Area, an area designated under s41(3) of the Wildlife and Countryside Act 1981, the Norfolk Broads or in a World Heritage Site, the satellite dish cannot be on a chimney, wall or roof slope which fronts a highway and is visible from a highway. For purposes of assessing whether a satellite dish is visible from a highway, if it is only screened by trees, bushes or other vegetation, it is considered to be visible from the highway. Also, on Article 1(5) land or in a World Heritage Site, a satellite dish cannot be on a building which exceeds 15 metres in height without planning permission being obtained.
In all instances if the satellite dish is installed on a building it must, so far as practicable be sited so as to minimise its effect on its external appearance and if it is no longer required it must be removed as soon as reasonably practicable.
If the dish does not meet any of these criteria, you need to make a planning application for it. Generally Sky, etc dishes are designed to meet these criteria, but if you are looking to install one to receive foreign television programmes, it is likely to require permission.