It is determined by Parliament, from someone in the line of succession.
In 1936 there was private, ministerial talk of Prince George, Duke of Kent, becoming King when Edward VIII abdicated, but it was decided in due course to stick with the person at the top of the line of succession, who was the Duke of York, who became George VI.
Current polls seem to actually support Charles being king next, not William.
Regardless, the succession is determined by the Succession Act and not any popularity contest.
Erm, wrong!
This is the beauty of Britain not having a written constitution.
Parliament does ultimately oversee the succession process; usually it does not intervene.
In 1936, Prime Minister Baldwin, at the time of the Abdication Crisis, told his Party's Members of Parliament: Cancel your engagements over the weekend, go to pubs and clubs and listen to what ordinary people are saying. A Parliament that listens to the ingenious ideas of elites behind closed doors and ignores the people is not doing its job.
A good Prime Minister will still wish to be made aware of what public opinion is about any su0ccession issue that might be regarded as problematic.
Once again, No. The Government did not interfere with the succession in any way. Prime Minister Baldwin and his government were firmly against the King marrying his once divorced and still married lover. He informed the King the Government would resign if he married Wallis.
Baldwin asked Churchill, in Opposition, if he would form a Government should he be called to. Churchill, a staunch supporter of the King, said no.
The King had three choices, marry Wallis and the Government woud resign, give up Wallis and reign, or Abdicate, marry Wallis and leave the country.
History records King Edward VIII's choice.
It is determined by Parliament, from someone in the line of succession.
In 1936 there was private, ministerial talk of Prince George, Duke of Kent, becoming King when Edward VIII abdicated, but it was decided in due course to stick with the person at the top of the line of succession, who was the Duke of York, who became George VI.
And don't forget the Palace ferretts. Talk is cheap and there was absolutely no way they could have pulled that off. They learnt that the Throne was not up for popular debate.
When King George died there was private, ministerial . . . yada, yada that perhaps Princess Elizabeth was too young to reign and perhaps the Duke of Windsor could become Regent until such time as she was old enough.(Probably when he died!)
History records that outcome of both of those sets of wannabe King Makers. The Act of Settlement takes precedent. It is bigger than any individual Government. It is the history of the Monarchy.
Should HM predecease Prince Charles I believe he will become Charles III because he has been called Charles for over 65 years. If someone called him something else he'd probably be looking over his shoulder for him.