Former prime minister Boris Johnson announced on Sunday that he will not stand in this week's Conservative Party leadership race to become the UK's next leader.
In a statement, Johnson said that while he had "cleared the very high hurdle of 102 nominations" from Tory MPs, the lack of unity in the Conservative Party meant that it was "not the right time" for him to run.
"Though I have reached out to both Rishi [Sunak] and Penny [Mordaunt] -- because I hoped that we could come together in the national interest -- we have sadly not been able to work out a way of doing this", Johnson added.
Former British Treasury chief Rishi Sunak announced his candidacy Sunday to become the next prime minister of the United Kingdom in a bid to "turn around" the country's economy and "unite" the Conservative party.
"There will be integrity, professionalism and accountability at every level of the government I lead and I will work day in and day out to get the job done," Sunak said in a statement.
Sunak has the backing of at least 124 Conservative lawmakers, according to unofficial tallies by the BBC and Sky News. That is well ahead of the 100 nominations required to qualify.
Sunak is the frontrunner in the Conservative Party's race to replace Liz Truss as prime minister.
The Conservative Party has ordered a contest that aims to finalise nominations Monday and install a new prime minister — the country's third this year — within a week.
Ex-cabinet minister Penny Mordaunt garnered about 24 lawmakers' public support so far.
Truss quit on Thursday after a turbulent 44 days, conceding that she could not deliver on her tax-cutting economic package, which she was forced to abandon after it sparked fury within her party and weeks of turmoil in financial markets.
Dozens among Britain's 357 Conservative lawmakers have not yet publicly declared whom they are backing to replace Truss.
Mordaunt has until Monday afternoon to garner 100 nominations.
If she meets that threshold, lawmakers will hold an indicative vote on the final two.
The party's 172,000 members will then get to decide between the two finalists in an online vote. The new leader is due to be selected by Friday.