Candidates released slick campaign videos on social media and appeared on Sunday morning political talk shows to make their cases to the public. Several promised tax cuts, appealing to rank-and-file Conservative party members for whom low taxes are a mantra.
Johnson announced his resignation on Thursday after more than 50 members of his cabinet and lower level officials resigned from his government, many citing concerns that his ethical lapses had undermined the government's credibility.
That triggered the internal Conservative Party contest to pick a new party leader. Under Britain's parliamentary government, the next party leader will automatically become prime minister without the need for a general election.
International Trade Minister Penny Mordaunt and Foreign Secretary Liz Truss announced their bids on Sunday.
Mordaunt said the UK "needs to become a little less about the leader and a lot more about the ship." Truss pledged to reverse an increase in the national insurance rate and to "start cutting taxes from day one."
Former health secretaries Sajid Javid and Jeremy Hunt joined one of the most open leadership races in recent history late on Saturday.
Other contenders include frontrunner Rishi Sunak, the former Treasury chief, and Nadim Zahawi, who took Sunak's job as chancellor of the exchequer last week.
The race comes after Johnson, 58, was brought down by a series of scandals, the most recent involving his decision to promote an MP who had been accused of sexual misconduct to a senior position in his government.
An influential Conservative party committee is expected to lay out the rules for the leadership contest on Monday, with news reports suggesting that Conservative MPs will narrow the field to two before parliament breaks for its summer recess on July 21.
Party members around the country will then vote on the final choice before the end of August, the Times of London reported.
Johnson has said he will remain prime minister until his successor is chosen. But many want him to go now, with even some Conservative politicians worried that he could do mischief even as a caretaker prime minister.
As politicians took to the airwaves to endorse candidates on Sunday, many sought to distance their favourites from the turmoil of the Johnson years by stressing traits such as "integrity'' and "honesty".
Karan Bilimoria, the former president of the Confederation of British Industry, said the decision should be made as quickly as possible because businesses that are still struggling to overcome the impact of the pandemic and are now facing the growing possibility of a recession need help now.
"We have got to get through this period as quickly as possible and find a good leader who can then rebuild trust,'' he told Times Radio.
