Sajid Javid quit as Britain's finance minister on Thursday just weeks before the scheduled annual budget statement, in a shock move provoked by Prime Minister Boris Johnson's attempts to shake up his cabinet after Brexit.
The chancellor of the Exchequer said he had "no option but to resign" after Johnson offered to keep him on but only if he got rid of all his political advisers.
"I was unable to accept these conditions," he told reporters outside his home.
"I don't believe any self-respecting minister would accept such conditions and so therefore I felt the best thing to do was to go."
Javid was immediately replaced by his 39-year-old deputy, Rishi Sunak, a former investment banker and Brexit supporter who is seen as close to Johnson.
Former Brexit minister Steve Barclay took over Sunak's position as chief secretary to the Treasury.
The pound briefly retreated on Javid's departure but soon recovered as analysts said the new chancellor could open the way for more public spending and growth.
Sunak appears more aligned with Johnson than his predecessor in backing a looser fiscal policy, noted Paul Dales, chief UK economist at Capital Economics.
"The move seems designed to allow the government to push through even bigger increases in public investment and perhaps resuscitate tax cuts that previously looked dead in the water," he said.
But Javid's decision to quit rather than buckle to pressure also presents a challenge to Johnson's authority, just as he seemed at his strongest.
After his election victory in December, Johnson fulfilled his pledge to get Britain out of the European Union on January 31 -- but the country's future ties with the bloc remain uncertain.
- 'Stooge as chancellor' -
Johnson began his cabinet reshuffle by sacking his ministers for Northern Ireland, business, housing and the environment, as well as his attorney general.
Foreign Secretary Dominic Raab, Johnson's de facto deputy Michael Gove and several other key ministers stayed in post -- and Javid was widely assumed to be safe.
But there have been reports that the former City of London banker, born into a working-class Muslim family, had clashed with both the prime minister and his influential adviser, Dominic Cummings.
Javid refused to say whether the pressure came from Cummings.
Johnson's spokesman said a new economic team of special political aides had been formed to jointly advise both the prime minister and the chancellor.
Asked whether the planned Budget statement would still take place on March 11, he said only: "Extensive preparations have already been carried out for the Budget and they will continue at pace."
The main opposition Labour Party's finance spokesman John McDonnell said the government was "in crisis". Cummings had "won the battle to take absolute control of the Treasury" and appointed a "stooge", he added.
- Northern Ireland minister out -
Johnson had earlier sacked Northern Ireland secretary Julian Smith, a surprising move given Smith's role in restoring the power-sharing government to Belfast last month after a three-year suspension.
Smith helped persuade the two main parties, Sinn Fein and the Democratic Unionist Party (DUP), to work together for the first time since the executive collapsed in January 2017 in a scandal over a renewable energy scheme.
Irish Prime Minister Leo Varadkar led tributes to Smith's efforts, saying he was "one of Britain's finest politicians of our time".
His Foreign Minister Simon Coveney, who was also closely involved in the power-sharing talks, said that without Smith's leadership there would be no government in Belfast.
"You have been such an effective secretary of state for Northern Ireland at a time of real challenge and risk," he said.
Arlene Foster, who as DUP leader was restored as first minister of Northern Ireland under the deal, also hailed his "dedication to the role".
But The Times newspaper said Johnson felt "blindsided" by the deal because it includes an investigation into alleged crimes by British soldiers during decades of sectarian violence known as The Troubles.
Johnson appointed Brandon Lewis as Smith's replacement.
After years of political turmoil over Brexit, Johnson wants to focus this year on domestic issues, including investments in police, healthcare and infrastructure.
He used Thursday's reshuffle to announce Alok Sharma as his new business and energy minister, with a new responsibility for running the UN climate talks in Glasgow in November.
Claire O'Neill, the former president of the so-called COP 26 summit, was sacked last month. She subsequently warned that planning for the summit was "miles off track".