Boris Johnson Prime Minister of Great Britain was diagnosed with having COVID-19 about 10 days ago. Today there is an announcement that the Prime Minister has been moved into "intensive care".
I did a web search to look for info on GBs system for "order of succession" and was shocked to discover the following:

Johnson’s hospitalization raises a grim question: Who in the UK government takes over if the prime minister becomes incapacitated, or even dies? Some countries have succession plans that are set in stone. The UK does, too, but it’s reserved for its monarch. If Johnson is no longer able to carry out his duties, it’s not clear what happens next. He is not the head of state in the UK, and his role is a matter of convention rather than constitution.

I would be very interested to get the perspective on this from anyone but particularly those who are or were citizens of England/Great Britain.