The ACBS (Advisory Committee on Borderline Substances) is a non departmental public body, owned by the Department of Health. Its job is to recommend to GPs which products that are not drugs or medical devices can be prescribed to patients.
 
If you want to have your product listed on the prescribable list, it must be approved by the ACBS Committee. The products do not need ACBS approval to be sold in the UK, but they cannot be prescribed by a GP without ACBS approval.

You can find further information on the Department of Health website.