Rishi Sunak calls for stability and unity as he wins contest to be PM
Rishi Sunak, who will become the next UK prime minister within hours, has issued a plea for unity in the face of a "profound economic challenge".
He won the Tory leadership contest  after rival Penny Mordaunt failed to secure enough backing from MPs.
In his first speech, Mr Sunak said bringing his party and the UK together would be his "utmost priority".
Mr Sunak, 42, will be the UK's first British Asian prime minister and the youngest for more than 200 years.
Mr Sunak - a practising Hindu - is expected to take office later this morning after being formally appointed by the King.
He replaces Liz Truss, following her resignation just 45 days into her tumultuous premiership last week.
After chairing her final cabinet meeting at 09:00 BST, the outgoing prime minister will make a statement outside No 10 before travelling to Buckingham Palace for her final audience with the King.
will be followed by Mr Sunak's first audience with the monarch, during which he will be invited to form a government. 
He will then travel to Downing Street to make a statement at about 11:35, before entering No 10.
President Joe Biden has said he plans to call Mr Sunak to "offer his congratulations" after his meeting with the King, the White House Press Secretary said.
Mr Sunak takes office as the third Conservative prime minister since the party won the last general election in 2019 - prompting Labour to lead calls for an early general election as a result.
In his speech on Monday - which took place behind closed doors - Mr Sunak told Tory MPs this was going to be a tough period and ruled out an early general election, MP Simon Hoare said.
former chancellor said the Conservative Party, trailing Labour in the polls by huge margins, was facing an "existential threat", but could win the next election by uniting.
ree MPs in the room told PA Media news agency Mr Sunak's message to the party was "unite or die", as they focus on delivering on the public's priorities during a cost of living crisis.
Former Tory leader Iain Duncan Smith, who backed Liz Truss in the summer leadership contest, said it would be "really dangerous" for the party to continue internal rows.
"It's time to make sure we govern and get the decisions right again," he told BBC Radio 4's Today Programme.
Later, in a TV address that lasted less than two minutes, Mr Sunak promised to serve with "integrity" and thanked outgoing Prime Minister Liz Truss for leading the country during "exceptionally difficult circumstances".
"The United Kingdom is a great country but there is no doubt we face a profound economic challenge," he said. "We now need stability and unity and I will make it my utmost priority to bring our party and our country together."
Mr Sunak's coronation, in effect, as Tory leader caps a rapid political comeback by the former chancellor after he lost out to Ms Truss in the last leadership contest during the summer.
Ms Truss - whose tax-cutting agenda Mr Sunak dismissed as "fairytale economics" - tweeted to congratulate him and offer her "full support".
Her successor will take office at a time of economic crisis and pressure on public finances, exacerbated by Ms Truss's mini-budget, most of which has been scrapped.
Watch: Rishi Sunak makes first public address since winning Tory leadership contest
Mr Sunak's leadership rival Penny Mordaunt withdrew from the latest contest minutes before the result was announced, admitting it was "clear that colleagues feel we need certainty today".
"This decision is an historic one and shows, once again, the diversity and talent of our party," Ms Mordaunt said. "Rishi has my full support."
Ms Mordaunt took the leadership race to the wire, but came under pressure to unite behind Mr Sunak after former Prime Minister Boris Johnson withdrew from the contest on Sunday.
Mr Johnson - who resigned as prime minister only seven weeks ago - claimed he had enough support to stand but acknowledged now was "not the right time".
Sources told the BBC that Mr Sunak and Mr Johnson met on Saturday as Tory MPs decided who to back in the second Tory leadership contest in four months.
Mr Sunak was chancellor in Mr Johnson's government and within weeks of taking the role had to steer the UK economy through the Covid-19 pandemic.
But he quit as chancellor in July after the government was dogged by scandals, giving momentum to a cabinet mutiny that forced Mr Johnson from office.
First elected as an MP for the constituency of Richmond in North Yorkshire in 2015, Mr Sunak has experienced a meteoric rise to the apex of British politics.
Before becoming an MP, Mr Sunak worked in finance and is thought to be one of the richest MPs.
But his family's finances came under intense scrutiny earlier this year, when the tax affairs of his wife, Akshata Murty, were placed in the spotlight.
Age: 42
Place of birth: Southampton
Home: London and Yorkshire
Education: Winchester College, Oxford University, Stanford University
Family: Married to businesswoman Akshata Murty with two daughters
Parliamentary constituency: Richmond (Yorkshire)
Opposition parties have been clamouring for a general election, arguing that Mr Sunak does not have a democratic mandate to become prime minister.
Mr Sunak will be the fourth consecutive prime minister - after Theresa May, Mr Johnson and Ms Truss - to take the role of leader without a general election, although Mrs May and Mr Johnson both won general elections as PMs in 2017 and 2019.
xt general election is not due to take place until January 2025 at the latest, after the Conservatives won a landslide majority in 2019.
Mr Sunak is under no obligation to call an early election under the UK's parliamentary political system. 
Labour's Pat McFadden, shadow chief secretary to the Treasury, said the Conservative Party has brought "instability and chaos". 
"The party [Mr Sunak] represents is part of the problem, not the solution," he told BBC Breakfast. 
He argued the country needed a "proper, new government" rather than a "game of musical chairs at the top of the Tory Party". 
Liberal Democrat leader Ed Davey reiterated his calls for a general election, though accepted it was unlikely right now. 
"It's increasingly clear the Tories don't trust the British people," he told BBC Radio 4's Today Programme.
Scotland's First Minister Nicola Sturgeon said Mr Sunak should call an early general election and must not "unleash another round of austerity".