Answer:
The Prime Minister is elected by Parliament.
Step-by-step explanation:
In United Kingdom, the citizens' can directly vote for the president by themselves. They can only vote for the people who will represent each districts within the parliament body.
After the parliament body was elected , they will conduct their own voting on who will obtain the presidential seat. The party that have more seats from the parliamentary election will have higher chance of appointing their leader as the prime minister.