Paragraph 25 Minimum height
Without prejudice to the provisions of rule 5 of these Rules, in order to comply with the Instrument Flight Rules an aircraft shall not fly at a height of less than 1000 feet above the highest obstacle within a distance of 5 nautical miles of the aircraft unless:
(a)
it is necessary for the aircraft to do so in order to take off or land;
(b)
the aircraft is flying on a route notified for the purposes of this rule;
(c)
the aircraft has been otherwise authorised by the competent authority; or
(d)
the aircraft is flying at an altitude not exceeding 3000 feet above mean sea level and remains clear of cloud and in sight of the surface.