[Source of below information: Daily Telegraph  http://www.telegraph.co.uk/property/propertyadvice/propertyclinic/5917484/Property-advice-Certificate-of-Lawful-Existing-Use-or-Development.html]

John Winter explains what a CLEUD is

Yet another acronym – what does it mean?

CLEUD stands for Certificate of Lawful Existing Use or Development. A distinction needs to be made between a CLEUD and a CLOPUD (Certificate of Lawfulness Of Proposed Use or Development). The former confirms that an existing use is lawful, whereas the latter seeks to ascertain, from the local authority, whether a certain proposed use is permissible. Planning law is intricate and can have pitfalls for the unwary so applicants are advised
to discuss the situation with the planning officer before applying for either.

In what situation might I apply for a CLEUD?

You might be worried that the use of a piece of land or a building is not in accordance with a valid planning consent, or that it could be in contravention of conditions that have been attached to a consent. To set your mind at rest, you can apply for a CLEUD; if granted, this regularises the use.

One reason for doing so is the worry that the local authority may take enforcement action against a dubious use. But this may be entirely unnecessary as the authority is severely circumscribed in its powers. It can serve an enforcement notice in the event of a piece of land or a building being used for a purpose which is not lawful but it has to do so without undue delay because the law imposes a strict time limit. This expires after four years for most domestic situations and 10 years in other cases. Thus, once the time limit is past, a non-conforming use, work done without planning consent and a breach of a condition attached to a consent all become legal.

If I still want to get a CLEUD, how do I go about it?

The process of applying for a CLEUD is, in many ways, comparable to making a planning application, with the same need to pay a fee and opportunity to appeal if the decision does not go your way. Circular 10/97 recommends the applicant to be very precise in defining the land that is the subject of the application for a CLEUD, or in describing the existing use of the land. If consent is granted on the basis of an application containing a materially false statement, then the local authority may revoke the CLEUD and the applicant will have committed a criminal offence.

In extreme cases, the authority can serve an enforcement notice on the non-conforming piece of land or building and require it to be put back to a pre-existing condition.

The local authority is obliged to keep a register of all CLEUDs that have been issued within its area.