With the Conservative party struggling to navigate Brexit, Labour is pressing the point that Jeremy Corbyn is ready to step in as prime minister. But while Labour is quite justified in presenting itself as the alternative minority government, this isn’t likely to happen without a general election.
The prime minister is appointed as the party leader most likely able to command the confidence of parliament. Changes of prime minister can take place without an election, so on that front Labour is right that the Queen could, theoretically, call on Corbyn without an election.
In the UK, a prime minister does not automatically need to have a coalition or confidence and supply agreement in place. They do, in the end, need to be able to pass certain money and supply bills in order to fulfil the two most important functions of government: collecting taxes and paying for services. And they need to be able to survive no-confidence votes that will otherwise trigger a new general election.
Minority governments can get legislation through on a case-by-case basis, which is one reason why the current Conservative government can remain even if their confidence and supply agreement with the DUP breaks down. But it is also a reason why Labour can argue that it should be in government now, even if it is well short of a majority through any parliamentary deal.
And even if Theresa May were forced out by her party, it is not a given that Corbyn would take over. It is true that if the Queen needed an alternative there are many precedents for looking to the opposition (it happened in 1923-24 when a hung parliament split the vote between Liberals, Labour and Conservatives).
But political realities still favour a Conservative successor. Should May fall, her advice as outgoing prime minister would be for a Conservative to take over. The Queen would not want in any way to be seen to be taking sides.
The Conservatives still have a higher seat share than Labour. And their much-battered confidence and supply agreement with the DUP still stands.
The Fixed-term Parliaments Act means May can reasonably survive most parliamentary challenges short of a motion of no confidence or leadership challenge. If she was brought down by a leadership vote, she would probably remain as prime minister until her successor took over. If it was a vote of no confidence in parliament, then we would have a general election anyway.
The less stable the Conservatives look, the more Labour’s argument that it is ready and waiting will gain traction. But the mechanics make it highly improbable without a general election.