Pay attention to what the next prime minister does, not what he says, in his first 24 hours

Whatever the outcome of the election, the incoming prime minister will want the first 24 hours to set the scene for their premiership. Boris Johnson or Jeremy Corbyn will make a speech outside Number 10, giving us their vision for their government. But past experience shows that it is their early decisions, rather than their first words as an election-winning prime minister, that give the best clue as to how the next premiership will unfold.

The speech is a moment of political theatre – but is rarely a good guide to what comes next

The speech outside Number 10 is a key moment for a new or returning prime minister. It is a chance to set out what they hope will be the key themes of their premiership. Whether it is Johnson or Corbyn making the speech, we can expect lots of talk about increasing public spending and improving public services – both recurring themes in the election campaign. And although the campaign has been light on Brexit detail, the government’s approach will surely be one of the key messages in the speech.

As we know, however, the speech does not always serve as a reliable guide to what will dominate the next prime minister’s time. Theresa May’s 2016 speech focused on the "burning injustices" that she wanted to solve, but her premiership was ultimately defined by her failure to build support for her approach to Brexit. David Cameron spoke about rebuilding trust in politics after the expenses scandal. However, he only mentioned the deficit once, and did not refer to Europe at all; arguably the two issues for which he will be remembered.

There are, however, better indicators to determine the next prime minister’s approach to government.

Who gets the big jobs in the first round of appointments or the reshuffle?

An incoming prime minister may want to rearrange their Cabinet – and changes are always likely on the lower rungs of the ministerial career ladder. Seeing who ends up in what jobs will point to the kind of government they want to present to the world – or where problems may arise. Theresa May placed some big rivals in key jobs, including the current prime minister as foreign secretary and David Davis as Brexit secretary. Their resignations over her Brexit strategy marked the beginning of the end of her premiership – will Johnson be able to command more loyalty?

And if Labour is leading the next government then there will be a big question about how many shadow ministers move into the roles they’ve been following for the last few years. While this would help new ministers to inherit policies with which they have some familiarity, Prime Minister Corbyn may, depending on the result, want to move people around. However, if new ministers need time to get up to speed with a new policy area then it will be more difficult for them to implement Labour’s ambitious programme of change.

Will the new prime minister announce any new departments?

Labour has lots of plans for new departments, while the Conservatives have not made any firm commitments (although there have been rumours about the Department for International Development being returned to the Foreign Office). The scale of any changes will probably depend on the size of the government’s parliamentary majority, or go out the window entirely if they are governing as a minority – creating new departments is hard work and can be a costly distraction, which the government may wish to avoid if it wants to focus on getting other business through Parliament. Labour has said it will rebrand the Department for Work and Pensions on ‘day one’, a move which would show that the new government is serious about big reforms to the much-criticised Universal Credit welfare system.

Creating new departments means other will be faced with closure. There is a limit on the number of Cabinet members, so if the next prime minister creates a new Cabinet job then he will have to get rid of one to free up the space. All eyes are on the Department for Exiting the EU – will it survive until the end of January if the Conservatives win? Or will it run Corbyn’s renegotiation with Brussels? The disappearance of a department also signals what the next government thinks is important, and what is less of a priority – Theresa May was criticised for removing ‘climate change’ from the name of any government department in 2016.

The early decisions which are made by the next prime minister will define his time in government, and what it means for the country, much more than any vision set out in his first speech. Once the dust has settled on Friday morning, it would be wise to focus on what he does, not what he says, to get a taste of what the weeks and months ahead will hold.