Permitted development rights take no account of a neighbour's 'rights to light'.
The UK planning system allows certain types of development to be made without the need to apply to your Local Authority for planning permission, this is referred to as 'Permitted Development'. Information relating to permitted development can be found on the Planning Portal
Planning applications often require professional advice in order to produce drawings, submit the application in the correct format, liaise with the Local Authority, all of which, in addition to the planning fee itself can prove to be expensive. There is also the possibility that the application may receive objections from neighbours/local residents, which will be taken into account by the Local Authority when making a decision on the application. All of this expense, stress and uncertainty can be avoided if the development is deemed to be 'permitted development'.
Whilst the advantages are clear for the party who proposes to undertake a project under permitted development, what about the rights of adjoining owners who may be affected in some way by the proposed development? For example, take a single storey side extension to a semi detached dwelling. The extension will be only 1.5 metres from the neighbours external wall (not the boundary), however the height of the extension will be 2.8 metres at the eaves (the junction of the top of the wall and roof). Although the extension will impact on the available light from the neighbours kitchen windows, this is classified as permitted development. The photograph below shows the new extension on the left hand side.
Permitted development rights take no account of a neighbour's 'rights to light'. Therefore it is currently acceptable under UK planning laws for a development that does not require planning permission (as it may be permitted development) and is therefore deemed as acceptable, to adversely affect the right of an adjoining owner. This, surely cannot be acceptable.
Any adjoining owner who is affected in this way will receive little help or guidance from the Local Authority because as far as they are concerned this is permitted development and there is nothing they will do apart from unhelpfully tell you to complain to the Secretary of State.
All is not completely lost however, as there is a law that may provide a way of challenging 'loss of light' (Prescription Act 1832). If a new building limits or reduces the amount of light coming through windows and when measured the level of light falls outside 'acceptable levels', this could then be deemed to be an obstruction. If this is the case then you may be able to take legal action against the party who created the obstruction.
If you think you may have a case in respect of the above you must first think very carefully and weigh up the possible benefits of starting legal proceedings. Do not be under the impression that if you are successful that your neighbour will be required to remove or make significant alterations to their development. This is only likely to happen in extreme circumstances where the developer has constructed outside the requirements of permitted development, or has breached other statutory requirements. The general outcome of cases of this nature is that the development will remain and the court may apportion a certain level of compensation for the general reduction of light.
In conclusion, in certain circumstances permitted development appears to disregard the rights of adjoining owners, and at present there is very little that can be done to stop this happening. In a 'free' society like the UK this does seem to be unacceptable, and maybe it is now time for permitted development guidelines to be amended to close this loop hole.