(politics,UK) A more formal title for the Official Opposition (the largest opposition party) in the House of Parliament, used when there is a king on the throne.
2023 March 8, Christian Wolmar, “Labour passes up the chance to deliver a forceful rail policy”, in RAIL, number 978, page 35:
The job of His Majesty's Opposition - especially as election time looms - is to provide well-worked-out alternatives to government plans, not to acquiesce in what could prove to be a disastrous policy for rail passengers.
