The ECA has released advice on archiving documents. This includes guidance on how long certain information should be kept on file.
Documents such as title deeds, planning permission and building regulation approvals should be stored until the property has been sold. Information relating to contracts not executed as a deed ie a simple contract, bind the contractor to liability limited to six years. It is expedient to hold these documents for nine to ten years.

For contracts that are executed as a deed, papers should be kept for up to 16 years. This is for the liability period of 13 years plus a latent defects period.

Documents such as board or partnership minutes, insurance policies and pension particulars should be archived for at least 40 years.

Source

Electrical and Mechanical Contractor