Unless the packaging itself is being physically consumed, packaging materials are outside of the scope of the BRC Food Standard. There may be some borderline examples, but I can't think of any.
At the back of the Food Standard there is a list of the food categories, which is periodically updated by the BRC, and it is this that the Certification Bodies use when determining how and by which auditor the audit is organised.
There is nothing wrong with taking some of the best practice from the Food Standard and developing your systems around these, but a Food certificate issued against a packaging material is likely to be invalid.