4. A charging scheme may provide for charges as are reasonable or necessary to meet the requirements of paragraph 6, and may in particular provide for different charges to be payable according to:
(a)the description of the authorisation in question;
(b)the controlled activity in question;
(c)the scale on which the controlled activity is carried on;
(d)the description or amount of any substance to which the controlled activity in question relates;
(e)the number of different controlled activities carried on by the same person.