Used for high-ranking officials to signal respect and formality in politics. In Parliament, members address each other as 'the Right Honourable' for politeness.
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Not Always British
While British in origin, some Commonwealth countries also use this honorific for officials. The Right Honourable Jacinda Ardern addressed the New Zealand Parliament.
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Reserved Usage
Do not use 'Right Honourable' casually or for people who do not hold the officially recognized positions. Only call the Speaker of the House 'the Right Honourable' officially, not your neighbour.