The Prime Minister of the United Kingdom is the leader of His Majesty's Government. They chair Cabinet meetings. It is the highest civil office in the United Kingdom.
The procedure
The appointment of a prime minister by the monarch is based on advice. However, though the advice is technically informal, the monarch would create a constitutional crisis if they did not comply. Therefore, in practice, what is decided in the House of Commons is the decisive event. The voters elect Members of Parliament (MPs), and the MPs choose the prime minister. The system grew in stages as the Commons grew in power and the monarch's authority dwindled. The current prime minister has been Rishi Sunak since 25 October 2022.