You will need to put together a heritage statement for any application affecting a listed building, unlisted building in a conservation area, a locally listed building, a registered historic park or garden.
Applications for listed building consent, or planning permission where the proposal affects a listed building or heritage asset, should be accompanied by a statement of significance. This is more commonly called a 'heritage statement' and is a validation requirement.
You can either produce this statement yourself, or approach a consultant to preparing this on your behalf. It only needs to be proportionate to the work you are undertaking and significance of the asset and you should always consult the listing description which can be on the National Heritage List for England (NHLE).
We have produced a short guide to help you prepare a heritage statement.