This is the key to any development for without it you cannot legally build unless you are building within ‘the permitted development’ rights. The Planners are concerned with many aspects such as parking, overlooking, use, of materials, etc.
Please note that planning applications typically take 2-4 months for the Council to process depending largely on whether neighbours object or not. Prior to making a planning application it is worth discussing proposals with the Planners to check the relevant policies and views and also to discuss proposals with neighbours to try and resolve possible objections which can at least cause a delay.
When any planning application is made, the Planners will make their recommendation. If no contrary views are received the Planners will then normally issue a planning decision using their delegated powers – some Local Authorities operate slightly differently. If a contrary view is expressed (e.g. from a neighbour or Councillor) then the proposals will normally go before the Development Control committee made up of elected Councillor Representatives for their decision, which can over-rule the Planners.
If a planning refusal is the outcome there is then the opportunity to appeal to the Secretary of State for the Environment but this can take 2-6 months and may agree with the planning decision, so if at all possible it is best to submit a scheme that is a compromise between planning policy and your requirements.
The above notes are for preliminary guidance only and are far from being exhaustive. Each individual client and property will almost always involve the need for more specific advice, for example if the property is in a Conservation area, is Listed, or is of a certain orientation to neighbours that may have an affect on neighbouring properties etc.