Outgoing British Prime Minister Boris Johnson is not ruled out as a minister in Lizz Truss's cabinet if she wins the leadership race, according to UK Secretary of State for Education James Cleverly, a close ally of Truss's, The Telegraph reported.

Truss served as Foreign Secretary in Boris Johnson's cabinet, and the two were close allies throughout Johnson's tenure.

Cleverly believes that Johnson could remain in UK politics at a senior level and would be "comfortable" with serving in Truss's cabinet if she approves him, the newspaper added.

A senior source in Truss's campaign refused to comment on whether Johnson could serve in her government, saying she was "not making any plans at the moment" about her cabinet appointments, The Telegraph revealed. 

Conservative rivals Rishi Sunak and Liz Truss will compete in the coming weeks for the premiership after the Tory party's lawmakers held the last vote Wednesday.

The crucial race for second place was narrowly won by Foreign Secretary Liz Truss on 113 votes, against 105 for former Defence Secretary Penny Mordaunt.

Sunak and Truss now take their case to Conservative party members, who will decide the new leader and prime minister after a series of nationwide hustings in August. The result will be announced on September 5. 

Sunak's resignation as Finance Minister this month helped to topple outgoing leader Boris Johnson after months of scandal including "Partygate".

Johnson announced that he would step down after a slew of resignations hit his government earlier this month in protest of his leadership. He will, however, stay as Prime Minister until a replacement is found.

At his last session of Prime Minister's Questions in the House of Commons earlier Wednesday, Johnson bowed out by saying "Hasta la vista, baby!"

In a hint of support for Truss's low-tax platform, Johnson urged his successor to "cut taxes and deregulate where you can to make this the greatest place to live and invest."

Truss tweeted that she was "ready to hit the ground running from day one."

But whoever wins the Tory race, "like some household detergent, would wipe the floor" with the main opposition Labour party, Johnson predicted.