Sunak, 44, was facing the impossible challenge of overcoming voter anger against the incumbent Tories after 14 years in power. The 61-year-old Keir Starmer-led Labour Party, meanwhile, maintained a strong lead over the Tories throughout the six-week campaign.
The 42-year-old frontrunner's tally continues to grow as former prime minister Boris Johnson flies back from his Caribbean holiday to reportedly also join the contest.
"I cannot deliver the mandate on which I was elected," she said speaking outside Downing Street.
Rishi Sunak on Monday is all set to make history on Diwali as Britain's first Indian-origin prime minister after being elected unopposed as the new leader of the governing Conservative Party, following Penny Mordaunt's withdrawal from the race.
If elected, 42-year-old Sunak will go on to make history as the first Prime Minister of the UK of Indian heritage.
The 42-year-old British Indian MP for Richmond in Yorkshire maintains his lead in the race to replace Boris Johnson as nominations formally opened for the contest.
The 42-year-old barrister, who until now served as the Attorney General in the Boris Johnson led government, was among the first contenders to throw her hat in the ring to replace Johnson as Tory leader and Prime Minister.
Foreign Secretary Liz Truss has extended a commanding 28 point lead over former British chancellor of the exchequer Rishi Sunak in the race to be the next leader of the Conservative party and the United Kingdom's prime minister, according to the latest YouGov survey.
Johnson now expressed his willingness to enter the PM race, saying he is "up for it."
With the former prime minister stepping aside on Sunday night saying it was "simply not the right time" for his comeback, the prospect of a Diwali victory for Sunak cannot be ruled out.
Indian-origin Rishi Sunak, who will take over as Britain's prime minister from Liz Truss, on Monday promised 'stability and unity' as his priority.
The former Cabinet minister received 114 votes in the first round of a secret ballot of Tory MPs held in the House of Commons, followed by United Kingdom foreign secretary Jeremy Hunt in second place with 43 and environment secretary Michael Gove third with 37 votes.
Glimpses from Liz's truncated reign as prime minister.
Sunak, who formally launched his campaign earlier, remains the frontrunner in the race with reportedly the highest number of MPs behind him.
Britain's BBC faced a mounting crisis as a row over football presenter Gary Lineker's criticism of government migration policy led to a presenter mutiny.
According to reports, the UK Foreign, Commonwealth and Development Office has invited Chinese President Xi Jinping as Head of State of a country with which the UK has diplomatic relations.
Outgoing Prime Minister Liz Truss will chair her final Cabinet meeting at 10 Downing Street on Tuesday morning before she makes her way to Buckingham Palace to formally tender her resignation to the 73-year-old monarch.
The 42-year-old is holding a solid 55 per cent lead with the Oddschecker betting odds aggregator, followed by a 29 per cent chance of former prime minister Boris Johnson making a comeback. Third placed in what is emerging as a three-way contest is Leader of the Commons Penny Mordaunt, who had polled third in the first round of parliamentary votes to shortlist candidates for the last leadership race.
Sunak, 42, has consistently topped the shortlist since voting began last week and on Monday he bagged 115 votes in the third round, which leaves only four candidates in the race.
With Rishi Sunak now firmly placed as the candidate to beat, the battle lines are drawn for second place in the race to replace Boris Johnson as Conservative Party leader and British prime minister, with the remaining five contenders set for their first public clash on Friday.
A survey of voters in Wakefield, who go to the polls for a by-election on June 23 to elect a new MP, suggests the Tories could lose by as much as 20 points.
Britain's Prime Minister-elect Liz Truss will spend Monday putting finishing touches to her new cabinet after being elected Conservative Party leader and is expected to unleash a complete shake up of outgoing leader Boris Johnson's top team.
The race to replace Boris Johnson as the Conservative Party leader and the British prime minister entered the final countdown stage on Friday, when voting officially closes for Tory members to choose between former chancellor Rishi Sunak or Foreign Secretary Liz Truss.
Rishi Sunak on Wednesday clinched his place for the final leg of the race to succeed Boris Johnson as leader of Britain's Conservative party and prime minister, and will go head-to-head with Foreign Secretary Liz Truss.
Rishi Sunak on Wednesday clinched his place for the final leg of the race to succeed Boris Johnson and will go head-to-head with Foreign Secretary Liz Truss as one of two finalists to take charge as Conservative Party leader and British prime minister.
Rishi Sunak on Tuesday scripted history when he was appointed by King Charles III as Britain's first Indian-origin prime minister after being elected unopposed as the new leader of the governing Conservative Party on Diwali.
The UK's prime ministerial race frontrunner, Rishi Sunak, spoke of his pride in what his Indian parents-in-law -- Infosys co-founder Narayana Murthy and Sudha Murty -- had achieved, as he fought back over media commentary around wife Akshata's family wealth.
The survey also shows a majority in favour of ousted leader Boris Johnson, with 55 per cent saying that Tory MPs were wrong to effectively force him to resign and 40 per cent saying they were right.
British Prime Minister Boris Johnson suffered a triple blow following crushing defeats for his Conservative Party in two important by-elections that also prompted the resignation of the party's chairman and one of his close allies, raising another major challenge to the embattled premier's leadership.
British Prime Minister Boris Johnson on Thursday finally agreed to step down as Conservative Party leader, triggering a leadership election for a new Tory leader who will go on to become the new premier, according to reports from Downing Street.
Former UK chancellor Rishi Sunak is closing the gap to catch up with rival, Foreign Secretary Liz Truss, in the race to 10 Downing Street, with only five points separating the two in a latest poll of the Conservative Party members on Tuesday.
Long queues were seen outside walk-in vaccination centres across the UK on Monday as people queued for their booster vaccine doses, even as the government's work from home guidance came in force as part of measures to tackle the "tidal wave" of the Omicron variant of COVID-19.
Newly-appointed British Prime Minster Rishi Sunak said on Tuesday that he has been elected to fix some of the "mistakes" made by his predecessor as he promised to place "economic stability and confidence" at the heart of his government's agenda.
Some believe that, as prime minister, Sunak will be particularly friendly to India and that he would return the Kohinoor and do similar gestures to his motherland. Such wishful thinking is not likely to materialise as he will act in the best interests of the UK and will not even appear to favour India, argues Ambassador T P Sreenivasan.
Sir Graham Brady, who is in-charge of collating the letters of no-confidence received by the 1922 Committee, said the threshold of 15 per cent of the Tory parliamentary party, or 54 MPs, seeking such a vote has been met and it will place on Monday evening in the House of Commons.
Sunak joins fellow Indian-origin candidate Suella Braverman, the UK Attorney General who is among the early Tory MPs to announce her plan to contest.
British Prime Minister Boris Johnson on Thursday said he was sad to announce his resignation as Conservative Party leader, triggering a leadership election for a new Tory leader who will go on to become the new PM.
Boris Johnson on Thursday spent about 35 minutes with Ashfield MP Lee Anderson who has since tested positive.
UK environment secretary Michael Gove became the latest Tory MP to announce his intention to challenge Johnson on Sunday.
A West Indian Day celebration, Hurricane Dorian destruction, and the immersion of Lord Ganesha in Mumbai round out this week's best images.