The current Prime Minister and incumbent is Boris Johnson of the Goldman Union of Capitalists, who won an electoral college landslide in 2016 against several political opponents. He is seeking for re election to extend his term. This is legal as per constitutional rights
Elections always happens in September and October (a specific date will be released in the process). Political Parties seeking to participate in the elections should have already elected their nominees in their respective conventions, which happens from December of the last year and ends by July and early August.
In the meantime, foreign nations and leaderships are allowed to endorse a political party of their own choosing, whether it's for ideological reasons or some other reason involved. Separate threads for the debates and the candidate's biographies and platforms will be created for convenience.