Brexit hardliner Boris Johnson topped the ballot by a landslide Thursday in a first-round vote for a leader to replace British Prime Minister Theresa May as the deadline for leaving the EU looms. In the ballot of Conservative MPs, former London mayor Johnson secured more than twice the number of votes won by his nearest challengers as three of the 10 candidates were eliminated from the race.

The outcome of the leadership battle could determine under what conditions Britain leaves the European Union. It is currently scheduled to leave on 31 October.

Johnson has said he is open to leaving the EU on 31 October without a formal deal between London and Brussels but would prefer to secure one by the deadline. Opponents of “no-deal” say it would cause economic chaos as Britain breaks up with its top trading partners.

Thursday’s vote was Conservative MPs’ first secret ballot in the governing party’s leadership contest. Johnson secured 114 votes, way ahead of Foreign Secretary Jeremy Hunt on 43 and Environment Secretary Michael Gove with 37. Former Brexit secretary Dominic Raab (27), interior minister Sajid Javid (23), Health Secretary Matt Hancock (20) and International Development Secretary Rory Stewart (19) also survived the cut.

Like Johnson, Raab and Javid have said they would not rule out a “no-deal” Brexit.

The seven candidates go through to Tuesday’s second round, when contenders will need the votes of 33 of the 313 Conservative MPs to stay in the contest. Former House of Commons leader Andrea Leadsom (11), ex-immigration minister Mark Harper (10) and former pension’s secretary Esther McVey (nine) failed to reach the 17 votes required to get through to round two.

May remains prime minister until a successor is chosen as head of the Conservatives. She stepped down as the centre-right party’s leader on Friday, having failed to deliver her plan for taking Britain out of the European Union after nearly three years in the post.

The list of candidates reflects the divergence of views within the ruling party on Brexit. Hunt and Gove are against leaving on no-deal terms in October. Hancock and Stewart are against leaving on no-deal terms in any eventuality.

May refused to say who she had backed in Thursday’s vote, telling reporters: “That’s none of your business!” Finance minister Philip Hammond also kept mum on his vote.

The contest so far has been dominated by revelations of Gove’s past drug-taking and bickering over the best way to resolve the Brexit impasse. But Thursday’s voting revealed each candidate’s current level of support. The two candidates most keen on taking Britain out of the EU without a deal were eliminated. McVey was pursuing a no-deal Brexit, arguing that the agreement May struck with Brussels keeps Britain too closely tied to the EU. Leadsom, runner-up to May in the 2016 leadership contest following the Brexit referendum, wanted a managed no-deal departure.

Harper had argued that an extension would be needed beyond the current 31 October deadline to secure a deal.

The battle will now be on between the remaining seven candidates to scoop up the trio’s 20 votes. Conservative MPs will keep whittling down the contenders until a final two remain. Grassroots party members then pick the winner, who will go on to become prime minister.

Assuming Johnson does not lose support, his tally is above the 105 votes required to secure a place in the last two.

The candidates face their first live television debate on Sunday in a 90-minute programme on Channel 4.

Conservative MPs will vote in a second ballot on Tuesday, when the contender with the fewest votes will drop out if they all reach the 33-vote target. After further rounds of voting next week, the party hopes to be down to the last two by the end of 20 June. After weeks of hustings around the country, the 160 000 Conservative party members then choose their favourite, with the result announced in the week beginning 22 July.

May will then step down as prime minister and the new leader of the largest party in parliament will be appointed as PM by Queen Elizabeth II.