John McDonnell will kneel for the Queen if asked to do so by courtiers when he is sworn as a member of the Privy Council.

However experts said this was unlikely, which will allow the shadow Chancellor to follow Labour leader Jeremy Corbyn and become an adviser to the Queen without having to kneel in the centuries-old ceremony.

The left-wing shadow Chancellor is due to join the Privy Council in coming days, which will allow him to be briefed on state secrets.

His friends said Mr McDonnell - who has expressed anti-Monarchist views in the past - was "very pragmatic about these things – he will just do whatever is asked of him".

Labour leader Jeremy Corbyn was heavily criticised for turning down his first opportunity to be sworn as a Privy Counsellor in October last year, preferring instead to go on holiday in Scotland.

Mr Corbyn eventually followed tradition and kissed the Queen’s hand, but specifically was allowed not to kneel, when he took part in the centuries-old ceremony in November.

In April this year it emerged that Mr McDonnell had “joked” that he wanted to see the public execution of members of the Royal Family – represented by papier-mâché models.

Mr McDonnell can be heard on a YouTube clip describing such action as “a useful form of street entertainment which might have balanced out the coverage of the Royal Wedding”.