How do we calculate the government's working majority?  

In practice, the government has a larger ‘working majority’. This differs from the simple majority because two groups of MPs do not vote in parliament.

Firstly, there is the Speaker and his or her deputies. While the Speaker is usually first elected to Parliament as a representative of a political party, they resign from their party upon election to the chair. This is because their role requires them to be non-partisan and impartial. The Speaker does not vote upon legislation in the House of Commons unless their vote is required to break a tied division.

The Deputy Speakers – of whom there are usually three – are also expected to exercise their role impartially and without regard to party politics. They do not vote in divisions either, but unlike the Speaker, they retain their party affiliations.

By convention, of the Speaker and Deputy Speakers, two are drawn from the governing party, and two from the main opposition party. This reduces the effective size of the Commons by four, to 646 MPs. The current Speaker, Sir Lindsay Hoyle, was elected as a Labour MP. Deputy Speakers have not yet been elected, but when they are, one will be a Labour MP and two Conservatives.

The second group of non-voting MPs in the House of Commons are the Sinn Féin members. Sinn Féin, a Northern Irish republican political party, rejects British political institutions and its MPs do not take up their seats in the House of Commons. The seven seats won by Sinn Féin in the 2024 general election bring the total number of voting MPs down to 639, meaning the government only needs 320 MPs to have a secure majority in parliament.