Try Rule 40 of the Rules of the Air Regulations 1996 -
(1) Subject to paragraph (2), the commander of an aircraft shall not make use of any radio navigation aid without complying with such restrictions and appropriate procedures as may be notified in relation to that aid unless authorised by an air traffic control unit.
(2) The commander of an aircraft shall not be required to comply with this rule if he is required to comply with rule 31.
Of course, this does not take account of approaches based on GPS information but, considering that's still not approved as a primary navigation aid in the UK, any approach procedure based solely on GPS is not permitted anyway.