The approved South Northants Local Plan states as follows:

Buildings are listed to protect and preserve them as
part of our heritage and to keep them unspoiled for
the benefit of future generations. The mechanism for
achieving this is a legal requirement imposed on
owners of listed buildings to obtain Listed Building
Consent from the local council (in this case SNC)
before any works are undertaken to demolish, extend
or alter the building in such a way as to affect its

It is a criminal offence to demolish, alter or
extend a listed building without obtaining Listed
Building Consent. Penalties are usually a heavy
fine (up to £20,000) or imprisonment.
The offence applies even if the Local Authority
would have subsequently approved the works.

Click on the above image to access the District Council's Supplementary Planning Guidance document dealing with Listed Buildings.