The reservation of data protection is by reference to the subject-matter of the Data Protection Act 1998 and Council Directive 95/46/EC:
Most of these provisions have been implemented in the 1998 Act.  However, the Directive contains some discretionary provisions which the UK has chosen to interpret in a certain way in the 1998 Act and it also sets out provisions establishing a Committee composed of representatives of the Member States.  The reference to the Directive is therefore included to ensure that all of those matters are reserved matters.
TABLE OF RESERVED MATTERS Head B - Home Affairs Details of Provisions