It’s difficult to make a case for social justice and equality on one bended knee, so my advice to Jeremy Corbyn would be to stay standing and to use his new position as a privy counsellor to make a couple of very clear statements about British democracy. First, that democratic values should be enshrined in all our institutions, top to bottom. Second, that for good, pragmatic and political reasons, our institutions need radical reform, starting with the abolition of the privy council.

Republicanism is not a left or right issue, the growing campaign to end the monarchy has plenty of supporters who voted Conservative and Ukip as well as Lib Dem, Labour, Green, SNP and Plaid Cymru. Yet it is undeniable that many on the left support abolition of the monarchy as part of a wider argument for equality. A recent poll showed that more than 60% of Corbyn’s supporters agree that the monarchy should go. So it would be unfortunate if the new Labour leader ducked a unique opportunity to challenge our rotten constitutional structures and the idea of hereditary public office, particularly after his principled decision to not sing God Save the Queen at the Battle of Britain commemorations.

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While I understand Corbyn’s pragmatic decision to accept an invitation to join the privy council, I would call on him to decline an invitation to go through the silly ceremony that new members usually submit to, getting down on bended knee to the Queen and kissing her hand. This absurd ritual flies in the face of Britain’s democratic values as much as it offends leftwing sensitivities. Corbyn would do well to let the palace know that while as a matter of courtesy he will meet the Queen, he will not be going through such rituals. He should suggest that such rituals are dispensed with altogether, as elected politicians owe their loyalty and obedience to the British people, not a hereditary monarch.

One day Labour will throw its weight behind the cause of republicanism and support the abolition of the monarchy. That day may be a step closer, but we’re not there yet. However, that doesn’t mean this moment can’t be used as an opportunity to call for the abolition of the privy council, and the scrapping of the royal prerogative, as well as an end to royal secrecy, the royal veto and a radical scaling back of royal funding. The privy council isn’t just a relic of a bygone era, but a fully functioning part of the machinery of government. It is where wide-ranging royal prerogative powers are given life, whether the signing of treaties, declarations of war or the significant powers of patronage granted to the prime minister. It is one of the least understood and most archaic parts of our government, and it has no place in a modern democracy.

The charity Justice spelt out the full extent of its powers and functions in an excellent report in which it described the privy council as “a problem of real substance, well beyond mere harmless and quaint ceremonial … a loophole in our constitutional safety net – a way in which hard law can be directly created, affecting fundamental rights, whilst bypassing Parliament and any prior accountability”.

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It is the powers that the crown gives our government that prompts even the most sceptical prime minister to become an ardent monarchist. That might explain the extraordinary lengths the government has gone to in protecting royal secrecy, exempting the monarchy from freedom of information laws, and why ministers agreed to a bizarre royal funding package while resisting calls for proper scrutiny that has left the taxpayer with an estimated £334m price tag. The cosy relationship between politicians and the monarchy may also explain why the royal veto has survived, a mechanism revealed by the Guardian, which allows Prince Charles to insist new laws give him unique exemptions and powers as Duke of Cornwall.

The claim from some quarters that Corbyn must join the privy council in order to receive security briefings is a fig leaf, a distraction that makes no sense. It’s quite possible to devise a method of ensuring confidentiality and secrecy without the pantomime of becoming a Right Honourable Gentlemen. The pantomime persists because it helps defend the power structures it represents.

I’m not expecting Jeremy Corbyn to announce plans to bring about the end of the monarchy just yet – he has said he doesn’t want to make it a priority. But Labour can start to call out the monarchy and the government on a range of important and related issues. These are issues of principle, probity and democratic legitimacy, issues that will significantly chip away at the foundations of a hereditary monarchy that is wrong in principle and bad for British politics. Corbyn’s invitation to join the privy council is an opportunity to challenge Britain’s most archaic of institutions. I hope it’s an opportunity he will seize with both hands.