Did you know that Elizabeth II, Queen of the Commonwealth realms, cannot be arrested in the UK whatever crime she might commit?
Historically, the general rule in the United Kingdom has been that the Crown has never been able to be prosecuted or proceeded against in either criminal or civil cases.
The position was altered by the Crown Proceedings Act 1947 which made the Crown (when acting as the government) liable as of right in proceedings where it was previously only liable by virtue of a grant of a fiat.
With limited exceptions, this had the effect of allowing proceedings for tort and contract to be brought against the Crown, but criminal proceedings are still prohibited from being brought unless expressly permitted by statute.
As the Crown Proceedings Act only affected the law in respect of acts carried on by or on behalf of the UK government, the monarch remains personally immune from criminal and civil actions.