Jeremy Corbyn has turned down an opportunity to be sworn in to the Privy Council amid continued uncertainty over whether he will declare allegiance to the Queen in person.
The Labour leader, a lifelong republican, had the chance to attend a meeting of the ceremonial body which formally advises the monarch - but declined, citing "prior engagements".
A spokesman refused to give details of the events, saying only that they were "private", but sources close to Mr Corbyn insisted it was not intended as a snub.
It was confirmed meanwhile that he will attend a State Banquet at Buckingham Palace later this month in honour of Chinese President Xi Jinping along with other senior politicians.
Guests at the white tie dinners are traditionally received by the Queen and the Duke of Edinburgh, shaking their hands and exchanging a few words of greeting.
Earlier it was reported that Mr Corbyn could avoid the need to swear an oath of allegiance in the presence of the Queen through a mechanism known as an Order in Council.
The Daily Telegraph said the Privy Council - including the monarch - could agree to appoint him as a new member without him being present.
In order for that to happen, the paper said he would still have to confirm that he had taken the oath but would not have to kneel before the sovereign.
Nevertheless, such a move would be highly controversial at a time when the Labour leader has seen his loyalty to Britain fiercely challenged by opponents.
He was widely criticised after he did not sing the national anthem at the Battle of Britain 75th anniversary commemorations.
In his speech to the Conservative Party conference on Wednesday, Prime Minister David Cameron accused him of a "Britain-hating ideology".
Tory MP Sir Alan Duncan, himself a privy councillor, said: "The Queen has always put herself above politics but Jeremy Corbyn seems to want to put his politics above the Queen.
"This is not so much about snubs, insults or ceremonies - it is more about whether Jeremy Corbyn wants to be a serious political figure or just a perpetual rebel."
Mr Corbyn was invited by Mr Cameron to join the Privy Council on becoming Labour leader last month.
Although its functions are largely ceremonial, membership does enable him to receive confidential intelligence briefings.
While Mr Corbyn is clearly uncomfortable with the more formal aspects of his role as Leader of the Opposition, his decision to attend the banquet for the Chinese president underlines how difficult they are to avoid.
The dinner will take place amid the splendour of the Palace Ballroom, and the guests will eat off antique china and drink from crystal glasses originally made for the Queen's Coronation in 1953.
The "recommended" dress code for men is white tie and tails, although it is not compulsory. A source close to the Labour leader said he had "no idea" what he would be wearing.