17. Nothing in regulations 15 and 16 shall have effect in relation to a prescription issued for the purposes of a scheme for testing the quality or amount of the drugs, preparations and appliances supplied under the National Health Service Act 1977 or the National Health Service (Scotland) Act 1978 and the regulations made thereunder or to any prescriptions issued for the purposes of the Medicines Act 1968 to a sampling officer within the meaning of that Act.