Retention of Planning Records - How Long to keep? - Public forum - Planning Advisory Service (PAS)

Basically i'm trying to find out how long do we as a District Council have to keep Planning Application Records/Files. I am under the impression that it is between 2-5 years but need an accurate answer. Consequently what is the rule/legislation for historical records? My understanding is that once a record has been kept for 30 years it then turns into an historical document. Do different rules apply for these?