I was just reading a post on Instagram in which someone from America couldn’t understand why, with the PM standing down, his deputy didn’t just step into his shoes.
The Institute For Government has a good explainer about the position of Deputy Prime Minister.
www.instituteforgovernment.org.uk/explainer/deputy-prime-minister-first-secretary-state
Unlike the US vice president, there is no constitutional deputy who automatically deputises for the prime minister or who would take over in the event the prime minister was incapacitated.
However, British prime ministers have sometimes chosen to ask another minister to act as their informal deputy. This de facto deputy has sometimes been given the honorific title ‘Deputy Prime Minister’ but at other times has been the First Secretary of State or the chancellor of the Duchy of Lancaster.
David Lammy was appointed deputy prime minister on 5 September 2025 following his predecessor Angela Rayner’s resignation. Lammy is also the Lord Chancellor and the Secretary of State for Justice.
[There is no current First Secretary of State. The post was last held by Dominic Raab who stepped up when Boris Johnson was admitted to hospital with Covid.]
[The current Chancellor of the Duchy of Lancaster is Darren Jones who I understand may stand against Burnham in a leadership contest.]
Deputy prime ministers have tended to play a more substantial role in Labour governments because the deputy Labour party leader is elected by party members and so has their own power base. However, the role of deputy prime minister and deputy Labour party leader are not necessarily always held by the same individual. The deputy prime minister is appointed by the Prime Minister whereas the Labour party deputy leader is elected by party members. Lucy Powell, the MP for Manchester Central, is the current Labour party deputy leader after being elected in October 2025.
Then there is the Deputy Prime Minister in a Coalition Government as Nick Clegg was to David Cameron. Nick Clegg described how the practicalities and dynamic of the 2010-15 coalition government shaped his role as deputy prime minister:
“I know the title was the same, but my role [as deputy prime minister] bore absolutely no relationship to John Prescott or Michael Heseltine… The Coalition Government couldn’t do anything unless both sides agreed. So we had to set up from scratch something which Whitehall has never done before, and certainly has not done since, which is create a sort of two-headed, bicephalous way of making decisions.”
[Imagine a Reform/Tory, Farage/Badenoch bicephalous arrangement … No, I don’t want to either. Both could start a fight in an empty room.]
Lots more in the IoG explainer but the key takeaway is that there is no constitutional deputy.