SARAH VINE: So how do you solve a problem like Prince Andrew?

What to do with bad Uncle Andrew? That's the pressing problem facing King Charles at his morning egg – and it's not an easy one to solve.

The latest batch of court documents revealing more lurid details of Prince Andrew's friendship with Jeffrey Epstein would test even the closest of brotherly bonds.

They repeat Virginia Giuffre's claims that Andrew sexually assaulted her three times when she was 17 and 18, including once during an orgy, and include testimony from one of Epstein's housekeepers that Andrew received daily massages while spending “weeks” at the home of the pedophile financier.

Despite all this, it is clear that Charles feels some degree of sympathy for his younger brother, who has vigorously (if not entirely convincingly) denied all allegations.

The appearance of Andrew and his ex-wife, Sarah Ferguson, along with other members of the royal family at church in Sandringham on Christmas Day would certainly imply as much.

But as king, Charles' first duty must always be to the Crown, as that of his mother was before him. And this new chapter in this miserable case might force him to think again. The way he responds could be the first serious test of his government.

Even though the specific allegations are never proven, Andrew's association with two sex offenders, Epstein and Ghislaine Maxwell, casts a shadow over the monarchy, and in particular the moral integrity of an institution that, thanks in large part to another troublesome sibling, , Prince Harry, has taken quite a beating lately.

No matter how absurd or implausible the allegations made by the Duke and Duchess of Sussex against senior Royals, no matter how difficult it is to prove what happened between Prince Andrew and Giuffre 20 years ago, the fact is that mud sticks. We live in a world where a mere accusation is enough to make people assume guilt, and where concrete evidence is not necessarily a requirement for a conviction in the court of public opinion.

The truth is that Prince Andrew is the gift that keeps on giving to those who want to get rid of the monarchy.

It doesn't matter how impeccably the rest of the Royals behave, how tirelessly they give their time to good causes, how cute the little boys are. With Andrew in the fold, their efforts will always be undermined.

Note how the anti-monarchist group Republic Andrew reported to Scotland Yard and called for a police investigation into the latest allegations. Note also how Sir Keir Starmer has said that where 'credible' allegations have been made, they should be investigated. In the past, Sir Keir has said that he 'often proposed the abolition of the monarchy'. Maybe now he sees his chance.

If King Charles wants to uphold his mother's legacy, he cannot afford to let his brother's past jeopardize the future of the Crown. He must distance himself and the institution from the object of these abhorrent accusations. He must make it clear that he takes these allegations seriously, and that while his brother deserves a fair trial, until and unless the case is satisfactorily resolved in his favor, he cannot expect to enjoy the trappings of a true Royal family.

As king, Charles' first duty must always be to the Crown, as that of his mother was before him. And this new chapter in this miserable case might force him to think again. The way he responds could be the first serious test of his government

It is crucial that the king cannot end up in a corner. He must act before he is forced to do so.

The late queen made a start by stripping Andrew of his HRH and removing him from royal duties. Withdrawing funding for the security of Andrew's home, the 30-bedroom Royal Lodge (the name is quite misleading: it's actually a palace), should be the next step.

Hopefully this would force him to move to the less flashy Frogmore Cottage, which, while not exactly a hardship by most standards, would at least be a step in the right direction.

But even that, I suspect, wouldn't stoke the boil. Because no matter how the king treats Prince Andrew, he will always remain Prince Andrew: entitled, arrogant and without any self-knowledge. Actually no different from Prince Harry. Two spare parts with the talent to make the rest even more spare.

And it shows every time he opens his mouth in public. Not just in that disastrous Newsnight interview, but also at Sandringham on Christmas Day when he asked Royal fans why they were there filming him. When it was explained that they thought the scenes were 'amazing' and 'beautiful', Andrew replied: 'You should come and stand on this side and see what it's like'. Argh. Talk about unkind.

I'm afraid there is no choice: Andrew must be out of sight and out of mind. I suggest a long-term stay on a Caribbean island, but given the circumstances that may not be ideal. Perhaps, instead of Frogmore, he could live quietly in Sandringham and host dinner parties for the hunting/shooting/fishing crowd. Just keep it away from the front port.