Post-election

Polls close at 10 pm and the votes are, in most constituencies, counted immediately. The earliest results are declared by about 11 pm, with most having been declared by 3 or 4 am; some constituencies do not declare their results until the following day. In Northern Ireland the count itself does not begin until the next morning, with results being announced from early afternoon onwards. When all of the results are known, or when one party achieves an absolute majority of the seats in the House of Commons, the first response comes from the current (and possibly outgoing) Prime Minister.

If a majority in the new Parliament has been achieved by their party, they remain in office without the need for reconfirmation or reappointment — no new term of office is started. If a majority has not been achieved, and it is obvious that the opposition has the numbers to form a government, the Prime Minister submits a resignation to the Monarch. The Monarch then commissions the Leader of the Opposition to form a new government. The Prime Minister has the option of attempting to remain in power even if seats have been lost. The subsequent Queen's Speech (i.e., outline of the proposed legislative programme) offers a chance for the House of Commons to cast a vote of confidence or no confidence in the government through accepting or rejecting the Queen's Speech.

The last Prime Minister who, having failed to win a majority, opted not to resign immediately was Edward Heath, in 1974. However, after initial negotiations with the Liberal Party failed to provide a coalition deal, he resigned, allowing Queen Elizabeth II to commission Labour leader Harold Wilson to form an administration. Until the Prime Minister reacts to the election result, either by deciding to remain on or resign, the Monarch has no role. Only if the Prime Minister resigns can the Monarch then commission someone else to form a government.

Thus Margaret Thatcher, who was Prime Minister from 1979 to 1990, was only asked to form a government once. Similarly, Tony Blair has only ever been commissioned to form a government once, in 1997. After each election, having remained in power, a Prime Minister may take the option to engage in a major or minor reshuffle of ministers. The largest party not in government becomes the Official Opposition, known as Her Majesty's Loyal Opposition. Any smaller parties not in government are collectively known as "the opposition".

Any vacancies created in the House, due to death, ennoblement, or resignation are filled by by-election. The time-frame for these is not automatic and they can be months after the vacancy was created, or even abandoned if there is a pending general election.