Labour leader Jeremy Corbyn is to be sworn in as a member of the Queen’s privy council today, according to the Palace.
The lifelong Republican will be expected to kneel and kiss the Queen’s hand and take an oath to serve her during a ceremony at Buckingham Palace.
He will swear to be a “true and faithful Servant unto The Queen's Majesty”.
Mr Corbyn put off the ceremony, which could have been conducted last month, because he said he had prior engagements.
After the rite is conducted the Labour leader will be known as The Right Hounourable Jeremy Corbyn, as members of the council are styled.
Council membership is generally given to Opposition leaders as well as MPs and peers in the Cabinet. Membership of the largely ceremonial advisory body is expected to allow Mr Corbyn access to intelligence briefings.
The ceremony's formal nature appears to sit uncomfortably with Mr Corbyn's relaxed anti-establishment image.
Since becoming Labour leader the long-time backbench rebel has however adapted his style to fit the duties of opposition leader: solemnly laying a wreath at the Cenotaph on Remembrance Sunday and wearing formal white tie to a state banquet with the Chinese President and the Queen.
The Queen is head of the Privy Council and the body advises her as she carries out duties as head of state.
The council also provides administrative support for the leaders of the Commons and Lords and has responsibility for the affairs of 400 institutions, charities and companies incorporated by royal charter.
It has a judicial role as the court of final appeal for UK overseas territories and crown dependencies and for a number of Commonwealth countries.
The body - the oldest form of legislative assembly still functioning in the UK - dates from the time of the Norman kings when the monarch met in private - hence the description Privy - with a group of trusted counsellors who fulfilled the role the cabinet performs today.
There are around 500 privy counsellors but not all members are required to attend the monthly meetings.
The gatherings usually consist of the Queen, the Lord President Chris Grayling and three ministers, plus any who are being sworn in. Discussions are held standing up, ensuring they do not last too long.
Additional reporting by PA
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