The Tory leadership contest will enter the next stage later when a second round of voting is held in Parliament.
Conservative MPs will vote by secret ballot in the Commons, with a result expected some time after 18:00 BST.
Any of the six remaining candidates will be eliminated from the contest if they come last or fail to secure at least 33 votes.
Those remaining in the race will take part in a live BBC debate in central London on Tuesday evening.
Further ballots are due later this week, where the bottom-ranked MP will be knocked out until only two candidates are left.
The final two names will then be put to a postal vote of the 160,000 Tory party members, beginning on 22 June, with the winner expected to be announced about four weeks later.
Former Foreign Secretary Boris Johnson remains the clear frontrunner in the race after topping the first ballot earlier this month with 114 votes.
Current Foreign Secretary Jeremy Hunt, who came second with 43 votes, and Environment Secretary Michael Gove, who was third with 37, should make it through to the next ballot on Wednesday if their support holds firm.
Former Brexit Secretary Dominic Raab, who received 27 votes, and Home Secretary Sajid Javid, who received 23, told reporters on Monday they were confident of making it through to the next round.
International Development Secretary Rory Stewart, who received 19 votes in the first ballot, said he had the necessary 33 backers to stay in the race “if they do what they say”.
Mr Stewart, who is currently sixth-placed among the remaining contenders, received a boost to his campaign on Monday evening with the endorsement of Cabinet Office Minister David Lidington.
Mr Lidington, who had backed Matt Hancock before he quit the race last week, told a rally for Mr Stewart there was a “yearning in this country for political leaders who tell it straight to people”.
“What Rory has done in his campaign is to demonstrate that there are no no-go areas in this country for him or for the party which he aspires to lead”, he said.
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– Has said he would consider a further delay to Brexit to achieve a better deal. – Plans to negotiate a “fullstop” to the Irish border backstop plan. He wants a free trade agreement, similar to the deal between Canada and the EU. – Would support a no-deal Brexit if he couldn’t get a better deal from Brussels.
– Would leave the EU with no deal, but it’s not his preferred option. – Wants changes to the Irish backstop and proposes sending a new negotiating team to Brussels. – Wants to make changes to the Withdrawal Agreement and thinks it’s possible to get them done by 31 October, but has not ruled out an extension.
– Would focus on making changes to the backstop. Would commission UK border force to work on solving the Northern Ireland border problem, paid for by the UK. – Says he cannot envisage circumstances in which he would want to have another extension to the UK’s exit date and the country must be prepared for a no-deal Brexit.
– Wants to leave on 31 October, the deadline for Brexit set by the EU, with or without a deal. He admits a no-deal exit will cause “some disruption” but says the “way to get a good deal is to prepare for no deal”. – Wants to remove the backstop from any deal and replace it with “alternative arrangements”. – Says he would withhold the £39bn “divorce” payment the UK is due to give the EU as part of the negotiated deal. He says the money will be retained until there is “greater clarity about the way forward”.
– Wants to re-open the withdrawal agreement for renegotiation in order to “overhaul the backstop”. – Says a new deal would include “the vast majority” of the deal Theresa May negotiated, but would replace the Irish backstop with “alternative arrangements” involving “advanced customs and trade measures” and checks away from the border. – Willing to leave on WTO rules, claiming it is “far better than leaving with a fatally flawed deal”, and will not rule out proroguing Parliament (essentially shutting it down) ahead of the 31 October deadline to prevent it blocking a no-deal Brexit
– Believes a no-deal Brexit would be “catastrophic” for the UK and is “undeliverable” and “unnecessary”. – He said it was unrealistic to believe the UK could get a new Brexit deal agreed by the EU and Parliament by the 31 October deadline. – Prefers trying to push through the current deal, agreed by Theresa May. However he says, if that failed, he would set up a jury of citizens to thrash out a compromise.
TAX AND SPENDING
– Says he wants to replace VAT after Brexit with a lower, simpler sales tax. – Wants to create the “most pro-business” tax regime in the world and put business at the heart of the revival of Britain. – Says he would not use the tax and benefits system to give the already wealthy another tax cut. – Says he would scrap the High Speed rail 2 project.
– As an entrepreneur, he wants to turn Britain into the next Silicon Valley, a “hub of innovation”. – Pledged to slash business taxes to the lowest in Europe to attract firms to Britain after Brexit and reduce corporation tax.
– Has promised to break from the austerity of the past nine years by slowing the pace of debt reduction. – Says this would free up about £25bn a year for spending priorities, including education. – Other money would be spent on local government and efforts to tackle crime, including an increase in the number of police officers by 20,000.
– Pledges to cut income tax for people earning more than £50,000 by raising the 40% tax threshold to £80,000. – Says it will benefit three million people and would cost £9.6bn a year. – Plans to pay for the cut partly from a pot set aside by the Treasury for a possible no-deal Brexit, and partly by increasing employee National Insurance payments.
– Wants to cut the basic rate of income tax from 20% to 15%. He suggests the basic rate falling by a penny a year. – Would equal a tax cut for the majority of UK workers. HMRC says there are currently 26.3m basic rate tax payers, but IFS says it costs about £5bn for every 1p cut in the rate of income tax. – Wants to raise the point that people start to pay national insurance to be the same as income tax, £12,501 a year. He says it would save the lowest paid workers £460 a year.
– Criticises other candidates for offering “cheap electoral bribes” to win support. – Says rather than being “straight” with people, his opponents have pledged “eye-watering” tax cuts worth £84bn.
HEALTH AND EDUCATION
– Says he wants to ensure the NHS is “fully-funded, properly funded” and that funding is protected under law. – Says he will spend £1bn extra on schools if he becomes prime minister.
– Mental health support in every school and a crackdown on social media companies that fail to regulate their content. – A cut in interest rate paid on tuition fees. – Long term plan to provide more funding for the teaching profession in return for a guarantee that no one leaves the education system without a “rigorous qualification” sufficient to work up to at least the average salary.
– Has suggested slowing down the rate of debt reduction, to release money for education. – Wants to see a “multi-year, multi-billion-pound boost” to spending on schools to “change the life chances of so many young people”.
– Promises to raise spending on secondary school pupils to £5,000 each. – Called the funding gap between some schools in cities compared to those in rural areas a “disturbing reality”. – Has previously said money spent on the EU could be put into the NHS.
– Says he is in favour of bringing back young apprenticeships for 14-16 year-olds. – Wants review of spending in Whitehall, with a “special commission” to look at public sector procurement, especially in the NHS. – Says he would “recycle roughly half” of the savings made by the spending review into frontline services, such as teachers and nurses.
– Pledges to invest more into education, especially for those in “mid-life”. – Vows to put a long-term plan in place to tackle the issue of social care in the UK. – Says people should not have to pay hospital car parking charges to visit a sick relative or wait four weeks for a GP appointment.
Mr Johnson has agreed to take part in the BBC TV debate, after missing a debate on Sunday night hosted by Channel 4.
His low media visibility in the campaign has attracted criticism from his rivals and their supporters.
However he picked up another cabinet endorsement on Monday, when Mr Hancock backed him as “the best candidate to unite the Conservative Party”.
The BBC debate – titled Our Next Prime Minister – will be hosted by BBC Newsnight presenter Emily Maitlis and broadcast on BBC One at 20:00 BST.
Candidates still in the leadership race will face questions from viewers across the country via local TV studios.