Former British Prime Minister Boris Johnson returned to Britain from holiday on Saturday to consider an audacious bid for a second term as prime minister in a race that could pit him against his former finance minister Rishi Sunak.

Potential candidates to replace Prime Minister Liz Truss, who quit on Thursday after six weeks in office, were embarking on a weekend of lobbying to secure enough nominations to enter the leadership contest before Monday's deadline. 

Johnson, who was on holiday in the Caribbean when Truss resigned, has not commented publicly about a bid for his old job. He has received the support of dozens of Conservative lawmakers but needs 100 nominations to be considered.

James Duddridge, British minister for international trade, said on Friday Johnson told him he was "up for it." He said on Saturday Johnson had secured 100 nominations, although a Reuters tally put him at just above 40 and Rishi Sunak, a former finance minister whose decision to resign helped bring Johnson down, at more than 110. 

The Sunday Times reported Johnson and Sunak could meet late on Saturday. It did not give details on any planned discussions. 

Only former Defense Minister Penny Mordaunt has formally declared she will run, although a Reuters tally showed she only had 22 nominations so far before Monday's 1 p.m. GMT deadline. 

Johnson is currently under investigation by parliament's Privileges Committee to establish whether he lied to the House of Commons over lockdown-breaking parties. Ministers found to have knowingly misled parliament are expected to resign. 

The contest has been accelerated to take only a week. Under the rules, just three candidates will be able to reach the first ballot of lawmakers on Monday afternoon, with the final two put to a vote on Friday that is limited to about 170,000 signed-up members of the Conservative Party.