Nominations are expected to open on Wednesday for the executive of the so-called 1922 Committee that sets the rules for leadership confidence votes. Johnson's critics hope to elect enough people to change the rules to allow another such vote before the 12-month grace period allows.

Johnson narrowly survived a confidence in vote in June.

Paul Brand, UK editor at ITV News, said he understood that a 1922 executive meeting would be held at 4 p.m. local time (1500 GMT) on Wednesday, to discuss rule changes.

The group would then meet an hour later with the deputy prime minister, Dominic Raab, Brand said.

(Reporting by Kate Holton; editing by David Milliken)