Johnson, who was forced out of office by his own Conservative Party over a series of scandals, urged the country to come together and back his successor.

Despite losing domestic popularity and eventually having been forced to announce his resignation, Johnson remains a cult figure in Kyiv for his support of Ukraine as it fights off Russia's invasion.

Four candidates remain, with one to be axed after a vote of Conservative Party lawmakers later on.

An initial field of 11 challengers has been whittled down following two days of votes by lawmakers, but no individual has yet emerged as the obvious successor to Boris Johnson.

It will only allow the opposition Labour Party to call a confidence vote if they remove reference to outgoing Prime Minister Boris Johnson from the motion to be voted upon.

A no-confidence motion means that lawmakers from all the parties represented in parliament can vote on whether the government, under Johnson for the time being, should continue in office.

The report from an investigation by senior civil servant Sue Gray is complete, but has not yet been submitted to Downing Street, the government says.