There is no minimum or maximum amount of information to be given in a fair processing notice. The Information Commissioner has said that it should be kept simple and easy to understand - see the press release at:
http://www.ico.gov.uk/upload/documents/pressreleases/2005/dp%20forum%207%20june%2005.pdf
he also has an FAQ at:
http://www.ico.gov.uk/Global/faqs/data_protection_for_organisations.aspx on 'what do I need to put in my fair processing notice....' which basically states that you need to outline what and how you will process information.