By Colin Talbot

A vote of confidence has been triggered in Theresa May as leader of the Conservative party. Many seem to assume that if a new leader was selected they would automatically become prime minister. But it's not necessarily true.

For that to happen, the new leader would have to be called upon by the queen to form a government. That will not happen unless she is advised that they can 'command a majority in the House'. But this will be a very open question.

The advice to the queen would come from two sources. The first would be the outgoing prime minister, who could probably be relied on to recommend her successor. The other would be her own private secretary, Edward Young, and the Cabinet secretary, Mark Sedwill. Their advice will be crucial. Above all they will not want the queen to be dragged in to deciding who forms a government between contending claims.

The problem arises from the fact that the Conservative party is currently a minority in the House of Commons, with only 317 MPs out of 650. They currently form the government with the formal support of the Democratic Unionist Party's ten MPs, giving them 327 votes.

Firstly, it's not clear whether that arrangement would still hold after a new Tory leader is installed. If it was a strong Brexiter then we can assume it will. If not, all bets are off.

Secondly, even if DUP support holds, it's not certain they will still have 317 Tory MPs. Several Tory members have already said that if Boris Johnson were elected Tory leader, for example, they will resign the party whip. At least half a dozen seem certain to do so, maybe more. So they could still be short of a majority.

The most likely scenario would be that the monarch's advisors would want push the issue back to the Commons. They could do this by calling on the new Tory leader to form a government but on the understanding that a vote of confidence, using the terminology of the Fixed Term Parliaments Act, would take place immediately to confirm it commands a majority in the House.

What will not happen is the suggestion put forward by Labour that they would be called upon to form a government. With only 257 MPs, Labour would have to show how they can form a majority in the House and that would involve corralling all the other parties and independents into some form of grand coalition. It's highly unlikely.

Final thought: May does not have to resign as PM if she loses the vote. She could quite legitimately say she will stay on as caretaker until the Tories have selected a new leader and they can be called on to form a government.

In short, we are potentially in for a prolonged period of uncertainty about who governs the UK.

Prof. Colin Talbot is part of a project at University of Cambridge called Brexit|Org|Gov which is monitoring organisational changes in Government and public services resulting from Brexit.

The opinions in politics.co.uk's Comment and Analysis section are those of the author and are no reflection of the views of the website or its owners.