Being prime minister means taking responsibility for how you shape your premiership 

A prime minister is rarely as strong as when they first take power. Their party believes in them. Ministers, owing their position to them, are responsive. They have a mandate, a plan and an opportunity.

Boris Johnson has already been prime minister for more than 100 days, but if he returns to office with a majority it will be the first time that he can call himself an election-winning prime minister. This would be a chance to reset his premiership. If Jeremy Corbyn gets into Number 10, this would be his first job in government – and the polls suggest that at best he would be governing in a tricky minority situation.

With the campaign now over, both Corbyn and Johnson will need to turn their mind to what the next task involves. And the experience of previous prime ministers suggests they would do well to reflect honestly on what they would bring to the role, should they make it to Number 10. What type of prime minister will they be – and how that will be shaped by their particular abilities, characteristics and, especially, flaws?

A prime minister must recognise their weaknesses and decide how to govern accordingly

How a prime minister starts their premiership depends on the circumstances of arriving in office. But it also depends on what they bring to the job.

How will they lead – and listen to – their Cabinet? Some prime ministers used it merely to sign off decisions that were discussed elsewhere, while others made it the key forum for making decisions. Margaret Thatcher came to dominate her Cabinets after setting out her preferred solution at the outset. Others abhorred Cabinet, with Tony Blair’s preference for smaller meetings seeing him accused of leading a ‘sofa government’. Whatever their approach, a prime minister must think how they manage this key meeting, as bad chairing will build up frustration with their Cabinet colleagues.

Prime ministers must also think how they make decisions. Are they any good at getting through the mountains of paperwork that Whitehall will send their way? Civil servants like decisiveness but they struggle with procrastination. But a prime minister must get those decisions right: U-turns and crises result from lack of attention.

And how will they manage the wider party? What are the dividing lines and where do the factions sit? Theresa May was ‘not clubbable’, and relied on her team to build relationships in Parliament. Johnson, unsurprisingly, brings more light-hearted energy to the Conservative Party’s 1922 Committee meetings with backbenchers. If the majority is small, or if either Corbyn or Johnson lead a minority government, then their whipping operation will be crucial.

The men and women who serve a prime minister can shape their premiership

A prime minister does not operate alone. Number 10 is tiny compared to the scale of some of the departments that are run by Cabinet ministers. To compensate, PMs will usually surround themselves by a large team. Prime ministers work closely with their chief of staff, communications team and policy advisers. This can be a source of strength and stability, or it can be the root of discord and disorder.

Some of the top team can be old friends – such as Anji Hunter for Tony Blair, or Ed Llewellyn for David Cameron – who know the prime minister better than anyone else. Other appointments can shape a premiership. From 1997, Alastair Campbell, in the newly-created role of director of communications, overhauled Whitehall’s press operation and enforced it through the notorious ‘grid’, co-ordinating the government’s plans on a daily basis.

But these appointments can easily alienate colleagues in Cabinet and eventually the wider party. Campbell would become the story as Blair’s government was accused of an obsession with ‘spin’; Gordon Brown sacked Damian McBride in 2009 after his press adviser was accused of hatching plans to smear Tory opponents; Theresa May had to discard Nick Timothy and Fiona Hill when she lost the 2017 general election and the party turned against the pair’s style and approach. By the time all had gone, however, they had shaped the premierships of the prime ministers they served.

Both Johnson and Corbyn work with controversial advisers. Both would be loath to work without them. But any prime minister needs to make sure that when their advisers speak on their behalf, it is what they want their government, the wider party and the public, to hear. Unclear responsibilities or in-fighting between advisers inevitably leads to dysfunction in Number 10 – and across government.

Taking on the premiership means taking responsibility

UK prime ministers have significant power. Through their management of Cabinet and the influence of Number 10 they steer a large machine ready to implement their government’s aims. There will be reasons why the job is harder than they hoped. The job of prime minister quickly becomes all-consuming. Events at home will knock the best-laid plans off course. The international stage will increasingly demand prime ministerial attention.

But, as Tony Blair put it, becoming prime minister means being "the person not explaining why things were wrong but taking the decisions to put them right". There can be no excuses. All prime ministers leave office with a sense of frustration at what they left undone, and what they could have done differently. But it is down to each prime minister to put in place the means for their own success.

Whoever is prime minister after this election – particularly if they win a majority – will be given the opportunity of a fresh start to shape their own premiership and put their promises into action. It is an opportunity which they won’t be given again.