It's an interesting point that the ANO 2005 states:
(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.
Which implies that all airfields that have chosen to dispose of their signal squares have no means to institute right hand circuits on any of their runways.
Note that the ANO states specifically 'ground signals' with no reference to RTF instructions, light signals. etc.
Mind you, there's little benefit in being dead right about these things, is there?