Prime minister Liz Truss has resigned after 45 days in the role.
A Conservative Party leadership contest will be held in the next week to find a successor.
The announcement comes after several of her own MPs called for her to resign, following ministerial resignations and U-turns on economic policies.
She was elected leader in September, meaning she has become the shortest serving British prime minister in history.

A contract has been awarded under Project Gigabit for 3,750 rural properties in Northumberland to get access to faster and more reliable broadband.
Borderlink Broadband, trading as GoFibre, has been awarded the £7.3 million contract and will work with the Department for Digital, Culture, Media & Sport (DCMS) and Northumberland County Council to provide gigabit-capable broadband to hard-to-reach homes and businesses.
Construction is set to begin near Berwick-upon-Tweed and Wooler in Spring 2023.

Suella Braverman has resigned as Home Secretary to be replaced by Grant Shapps.
Shapps was previously transport secretary and lost this position when Liz Truss became prime minister.
In her resignation letter, Braverman said she was quitting over a mistake she had made, sending documents from her personal email address.
She also criticised the government, saying: "Pretending we haven't made mistakes, carrying on as if everyone can't see that we have made them, and hoping that things will magically come right is not serious politics.