I didn't say in the circuit, I said in the ATZ.
ANO Rules of the Air Rule 17 (Rules for avoiding aerial collisions):
(5) Flight in the vicinity of an aerodrome
Without prejudice to the provisions of rule 39, a flying machine, glider or airship while
flying in the vicinity of what the commander of the aircraft knows or ought reasonably to
know to be an aerodrome or moving on an aerodrome, shall unless, in the case of an
aerodrome having an air traffic control unit that unit otherwise authorises:
(a) conform to the pattern of traffic formed by other aircraft intending to land at that
aerodrome, or keep clear of the airspace in which the pattern is formed; and
(b) make all turns to the left unless ground signals otherwise indicate.
i.e. unless ground signals (or radio information?!) indicate a RH circuit is in force. Though I admit that 'the airspace in which the pattern is formed' is not necessarily coterminous with the ATZ, I suspect a court would interpret it as such, in the absence of any other definition.
Tim