Jeremy Corbyn is facing fresh questions over whether he will pledge allegiance to the Queen in person after refusing an invite to be sworn into the Privy Council.
The Labour leader, a stanch Republican, turned down the chance to attend a meeting of the council on Thursday because of "private engagements", his spokesperson said.
Membership of the group is granted to the leader of the opposition to allow them to receive secret briefings from the security services.
Mr Corbyn's decision will increase speculation over whether he is willing to kneel before the Queen and swear an oath of allegiance to her - traditional protocol for when a new member is appointed.
The Islington MP could try to avoid the process altogether by joining the body without ever having to meet the Queen, according to The Daily Telegraph.
The newspaper claims Mr Corbyn may attempt to use a loophole which allows the Privy Council to appoint a new member without them being present - a method only previously used for members based overseas.
An unnamed member of the Council is quoted as saying:
A spokesperson for the Labour leader said no alternative date had yet been set for the process and that he was "unsure" about the protocol of by-passing the need to swear the oath on purpose.
Shortly after his landslide victory in the Labour leadership election, Mr Corbyn, 67, said he would have to consult with colleagues about how to approach the kneeling part of the ceremony.
"I didn't know that was involved actually....It's the first I've heard about it and I want to discuss that with colleagues, the whole process", he said.
Last month, Mr Corbyn was heavily criticised for not singing the national anthem at a Battle of Britain commemoration.
David Cameron accused Mr Corbyn of having "Britain-hating" ideology Britain in a highly personal attack in his speech to the Conservative Party conference on Wednesday.