The secret of the sovereign's success is her dullness. So argues the Queen's latest biographer AN Wilson, who writes that she inherited her 'vanilla' streak from her father and grandfather, and that "compared with any of her predecessors, she has been remarkably restrained in her expression of political views." Her heir, however, seems made from different DNA.

Prince Charles upset the apple cart before Christmas when, in his Radio 4 Thought for Day, he warned against "the rise of many populist groups across the world that are increasingly aggressive to those who adhere to a minority faith. All of this has deeply disturbing echoes of the dark days of the 1930s."

Although the broadcast was in a religious slot, several newspapers detected a coded political message and in particular a veiled reference to the rise of the far right in Europe and America. When over the Christmas period the Queen then missed two high-profile church services due to illness, this further fuelled speculation about the succession and how outspoken Charles might be as king.

The prince, of course, has form when it comes to committing political transgressions. Modern architecture, genetically modified crops and the ban on hunting with dogs have all been targets for his scatter gun. Some consider it constitutionally improper for the heir to the throne to fire off on such partisan issues, with the Daily Mail recently thundering "on all political matters he should keep his mouth shut – for his own good and the future of the monarchy."

But if the Prince of Wales persists in pushing constitutional boundaries to the limit, then maybe the solution is to change not Charles but the rules – by making them looser.

The sovereign, according to Walter Bagehot's formula, enjoys "the right to be consulted, to encourage and to warn". He must be above politics. What he cannot be is "an active and meddling fool who always acts when he should not". So the best sovereigns tend to be neither too dynamic nor imaginative. In other words, a little dull.

Bagehot chiselled these constitutional tablets of stone 150 years ago in an age of deference and non-disclosure. But are they still relevant in the era of Facebook and Freedom of Information (FOI) where nothing stays secret for long?

It was FOI that laid bare Charles's last political controversy when the Guardian's requests to publish his "black spider memos" were finally granted by the High Court in March 2015. The government had spent more than £400,000 resisting the disclosure with the then Attorney General Dominic Grieve arguing that the letters to ministers were "part of the Prince of Wales's preparation to be king."

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Britain's Queen Elizabeth delivers her speech during the State Opening of Parliament at the House of Lords, alongside Prince Charles in London on 9 May 2013 Getty

In the event, the black spiders proved harmless: just Charles crying wolf about a few of his pet causes from badger culls and support for beef farmers to the survival of the Patagonian tooth fish.

Many recipients of the letters lined up to say that they had no problem with Charles doing a spot of lobbying. The former education secretary Ed Balls wrote in his memoirs: "As far as his letters go, I always found him hugely, constructive and incisive... Anyone who objects to him playing that role is frankly wrong."

This suggests that Dominic Grieve had a point in defending the right of an apprentice king to make his views known to ministers. Where he was wrong, though, was to insist that it's done in secret. If the Prince of Wales is allowed greater latitude to sound off on non-party political issues, then the quid pro quo must be that he should debate them publicly.

All too often his political interventions have taken the form of asymmetrical warfare where his opponents are unable to challenge the royal knight errant in an open contest.

If Charles believes his views are valid, then they should be tested in a proper journalistic joust. Instead of just recording a message for Thought for the Day, wouldn't it be enlightening to hear Charles being grilled live on the Today programme by John Humphrys?

Now a fleet-of-foot speaker, the prince might actually hold his own far better than his media handlers fear.

This, of course, would be completely out of the question were he king. Or would it? Just because the Queen has never given an interview, there's no reason why her successor should follow suit.

On accepting the Sword of State, King Charles cannot at one fell swoop strike out from the record the political views he's publicly advocated for decades. Even if he remains tight-lipped when opening some hyper-modernist building, everyone would guess that he really thinks it a carbuncle.

Many Windsor watchers predict that Charles would be a more activist monarch than his mother. In what will likely be a short reign, he will want to make a difference and that would entail talking to the media.

If so, the rules governing a sovereign's right to voice an opinion might also need relaxing. This doesn't mean that he could ever challenge government policy or indeed advocate a position that might be construed as party political. But on broader matters – such as a key constitutional challenge facing the nation – maybe it would be healthy to hear what our head of state has to say.

Take the Scottish referendum in September 2014. For the Queen to get out her relatively innocuous message that "I hope people will think very carefully about the future," the palace – if a Whitehall source is to be believed – had to resort to the subterfuge of planting the overheard remark with a supposed bystander outside her Balmoral church who then reported it word perfectly to the press.

Yet during the devolution debate back in 1977 she was permitted to make a veiled public intervention, telling a joint session of parliament "I cannot forget I was crowned Queen of the United Kingdom of Great Britain and Northern Ireland. Perhaps this Jubilee is a time to remind ourselves of the benefits which union has conferred."

If there were a second referendum under a new monarch, it would surely be legitimate for the head of state to speak publicly – without taking sides – about the importance of such a vote for Scotland and the wider United Kingdom. After all, it could herald the break-up of the union.

The fact that one sovereign has ruled in an ultra-restrained manner for six decades shouldn't preclude her successor from loosening the reins to suit his new reign. Were this to happen, you can bet that Charles III's rule certainly wouldn't be dull.

David McClure is the author of Royal Legacy (Thistle Publishing)