STORY: So far 11 candidates have thrown their hat in the ring to succeed Johnson as leader of the ruling Conservative Party and prime minister after he quit following a dramatic rebellion by his own lawmakers and ministers after a series of scandals.
The 1922 committee of Conservative members of parliament (MPs) - which organizes the leadership contest - said hopefuls would need at least 20 nominations from the party's 358 lawmakers to even proceed to the first round of votes on Wednesday.
Anyone who then received less than 30 votes will be eliminated before another vote follows on Thursday.
Nearly all the contenders have promised extensive tax cuts to win over the support of their colleagues.
The field will be whittled down to a final two candidates by lawmakers, before a postal ballot of the Conservative Party's members, who number fewer than 200,000, takes place over the summer.