Certificates of Lawfulness or Lawful development certificates:

Are needed to ensure that your project or existing development is "lawful". In other words, the development is development against which no enforcement action may be taken and where no enforcement notice is in force, or, for which planning permission is not required. 

There are 2 types of lawful development certificate. A local planning authority can grant a certificate confirming that:

(a) an existing use of land, or some operational development, or some activity being carried out in breach of a planning condition, is lawful for planning purposes under section 191 of the Town and Country Planning Act 1990; 

or

(b) a proposed use of buildings or other land, or some operations proposed to be carried out in, on, over or under land, would be lawful for planning purposes under section 192 of the Town and Country Planning Act 1990.