LONDON (AP) — Boris Johnson's bid to become Britain's next prime minister was bolstered by fresh support from one of his former rivals Monday.

Health Secretary Matt Hancock threw his support behind Johnson, arguing that the former mayor of London's "unique personality" would help rally support around a deal to leave the European Union.

"Having considered all the options, I'm backing Boris Johnson as the best candidate to unite the Conservative Party, so we can deliver Brexit and then unite the country behind an open, ambitious, forward-looking agenda, delivered with the energy that gets stuff done," Hancock wrote in op-ed in The Times of London.

Hancock's endorsement came even though Johnson refused to take part in a televised debate Sunday night alongside his five rivals.

Broadcaster Channel 4 left an empty lectern for Johnson, who has a commanding lead after last week's first round of voting by Tory lawmakers in the contest to replace Theresa May.

May stepped down as party leader earlier this month after failing to secure Parliament's approval for her European Union divorce deal.

The House of Commons' 313 Conservative Party lawmakers will winnow the field of contenders in a series of leadership votes this week, with the final two names put to a postal vote of about 160,000 Conservative members nationwide. The winner, set to be announced in July, will become Conservative party leader and Britain's next prime minister.