On Thursday, the former prince Andrew became the first senior royal to be arrested in nearly 400 years – and he mightn’t want to look too closely at what happened to his infamous predecessor.

That was King Charles I, who was detained by forces aligned with parliament in 1647, convicted of high treason and executed on January 30, 1649.

After that, England endured the brutal chaos of Oliver Cromwell – and there was no monarchy for 11 years. Even once it returned, the so-called Glorious Revolution that followed in 1688 changed the throne forever.

Charles I believed he was above the law, and answerable only to God. He argued repeatedly during his trial that the court had no authority over him.

These days, the royal family is indeed answerable to the courts – although the King is not because they are his courts. The prospect of the King’s brother being tried in one of his own courts (R v. Mountbatten-Windsor?) must be daunting.

Royal biographer Robert Jobson said Thursday’s developments were seismic.

“We have to wait and see what comes out, and what the outcome is, before we know what the impact is on the monarchy,” he told Harpers Bazaar.

“It might not be a death knell, but it certainly might be a realisation that things have to be done differently and that there needs to be more transparency, more accountability at the heart of the monarchy, less deference, less dancing around it.”

Veteran royal commentator Richard Fitzwilliams said the arrest was “the institution’s ultimate test”. He said the situation with the former prince – brother of the King, the son of the late Queen Elizabeth II – was unprecedented.

“The royals will be under enormous pressure”, Fitzwilliams said.

“Every family has its horrors, but this has lasted for years,” he said.

Police at Wood Farm on Thursday, after Mountbatten-Windsor’s arrest. Photo: AAP

British police swept up to Andrew Mountbatten-Windsor’s home at Sandringham at breakfast time on Thursday (UK time), the former prince’s 66th birthday.

As he was taken away for questioning, police searched his current home, Wood Farm, and his previous residence, Royal Lodge, in Windsor.

Britain’s National Police Chiefs’ Council said it had “alerted operational colleagues within the Home Office of the arrest … “in line with routine practice”.

“This gave 30 minutes’ notice before Thames Valley Police made the arrest,” the NPCC said on Thursday.

However, Buckingham Palace was reportedly not notified.

Thames Valley Police said only that they had “arrested a man in his 60s from Norfolk on suspicion of misconduct in public office”.

“The arrested man has now been released under investigation,” they said in a later update.

The police investigation stems from Mountbatten-Windsor’s years as a British trade envoy. It follows revelations in recently released Epstein files that suggest he passed official government documents to the late financier.

Mountbatten-Windsor was forced to quit the trade role in 2011 amid growing concern about his friendship with Jeffrey Epstein, who had been sentenced to 18 months in prison in 2008 after pleading guilty to soliciting a minor for prostitution.

The former prince’s alleged crime could reportedly incur a sentence of life in jail. He has not been charged and has long denied any wrongdoing over his Epstein links.

Thursday’s bombshell update was followed quickly by one from the King.

“I have learned with the deepest concern the news about Andrew Mountbatten-Windsor and suspicion of misconduct in public office,” Buckingham Palace said in an official statement.

“What now follows is the full, fair and proper process by which this issue is investigated in the appropriate manner and by the appropriate authorities.

“In this, as I have said before, they have our full and wholehearted support and co-operation.

“Let me state clearly: The law must take its course.”

There are multiple reports, although no official word, that the Prince and Princess of Wales support the King’s statement.

Mountbatten-Windsor was held for about 12 hours on Thursday. While he was being questioned, the King met foreign dignitaries at London’s St James’s Palace, and attended the opening show of London’s fashion week. Nearby, the Queen went to an orchestral concert.

“Are you concerned about Andrew’s arrest, your Majesty?” she was asked as she left.

She waved but did not respond.

Journalist and royal commentator Afua Hagan said the royal family’s long tradition of “never complain, never explain” – famously espoused by the late queen – might not be enough.

“I don’t know if that’s how they get over it. I don’t know if that’s how they survive it,” she told the ABC.

“But that’s how they’re trying to go through this at the moment.”

Mountbatten-Windsor’s biographer, Andrew Lownie, said he thought the King had “grasped the seriousness of the situation”.

“I think the palace is basically saying to the police, ‘get on with it’,” he speculated in a video posted on social media.

Lownie said he believed authorities would pursue Mountbatten-Windsor “without fear or favour”.

“I think the police know there would be a public outcry if they didn’t do their job,” he said.

Mountbatten-Windsor was pictured slouched in the back of a vehicle as he was driven away from Aylsham police station on Thursday night local time in Norfolk, east of London.

Policing commentator Danny Shaw said it was hard to put a timeline on what happened next.

“It could be the Thames Valley [Police] are there, they’ve got everything they need, they just need to do a few questions, and they can make a decision very quickly with the Crown Prosecution on charging,” he told the BBC.

“You can’t rule out it moving very quickly.”

But he thought it was “much more likely” that everyone would “want to do things in an orderly manner and make sure that things are completely bottomed out”.

“My guess, and it’s literally nothing more than that, is that it will be weeks before any really substantial decision is made … as to whether this is something that needs to be taken further and into the court,” Shaw said.

-with AAP