Johnson extends lead in UK race for PM

Boris Johnson has increased his lead in the race to become Britain's next prime minister in the fourth round of the Conservative Party leadership contest.

Boris Johnson has won 143 out of 313 votes in the third round of the Conservative leadership race. (AAP)

Boris Johnson, the front-runner in the race to become Britain's next prime minister, increased his support among lawmakers in the fourth round of the Conservative Party leadership contest.

Johnson got 157 out of 313 votes. Environment minister Michael Gove came second with 61 votes, overtaking Foreign Secretary Jeremy Hunt, who got 59 votes.

Interior minister Sajid Javid was fourth with 34 votes and was eliminated from the contest. Two votes were declared invalid.

A fifth ballot later on Thursday will determine the final two candidates. Then Conservative Party grassroots members will decide who will become leader, and Britain's next prime minister, by the end of July.