Diana new investigation UK?

Only the monarch is exempt. All other royals are subject to the law like everyone else.

However, what makes anyone think that this "new information" has anything to do with the royals? If it does, where it has been for the past 16 years?

There was absolutely no motive for the royals to do away with Diana. The notion that they wouldn't have wanted her to marry a Muslim and considered the prospect so alarming that they resorted to murder doesn't hold water for a wide variety of reasons. It's utterly ridiculous.

The loony conspiracy theorists tend to claim that Prince Philip was behind it all, not the Queen and not Prince Charles. Philip isn't the monarch. Even if he were arrested and carted off to prison at the age of 92, it wouldn't likely have any effect on the succession. The Queen is not going to abdicate, Charles may or may not succeed her (depending on how long he lives), and one day, William will be king.

The Queen cannot be convicted in her own courts so whatever happens, she's safe. The rest of the royal family are not exempt. Princess Anne, after all, has been given speeding fines and been convicted for injuries caused by her dog.

We then have an interesting problem if Prince Charles is found to be involved and the Queen dies. There is no precedent for what happens if an imprisoned heir to the throne becomes monarch. I can only imagine that Parliament would have to step in and make William the Prince Regent so we've actually got a functioning head of state, or remove Charles from the throne altogether.

Who, Prince Charles and the Queen? I highly doubt it.