Video report by ITV News Political Editor Robert Peston
Ten contenders in the Tory leadership race have reached the first round of voting by MPs, with only one candidate failing to gain sufficient support.
The candidates, announced by joint acting chairman of the backbench 1922 Committee Dame Cheryl Gillan, were: Boris Johnson, Jeremy Hunt, Michael Gove, Sajid Javid, Rory Stewart, Dominic Raab, Matt Hancock, Andrea Leadsom, Esther McVey and Mark Harper.
Outsider Sam Gyimah, the only contender open to a second referendum - -pulled out the race just before the deadline, citing a lack of backers and lack of time to "build sufficient support".
The MPs - who each had the backing at least eight of their colleagues - will need at least 17 votes to get through the first ballot on Thursday - while the candidate with the lowest votes will be eliminated.
Analysing the successful bunch of candidates, ITV News Political Editor Robert Peston said "this is not perhaps the best representation of modern Britain".
The group only includes two women and one person from an ethnic minority, with six of the candidates having attended the elite Oxford University and two attended the even more prestigious Eton College School.
ITV News Political Editor Robert Peston said the "biggest test" any of the candidates faced on Monday was Michael Gove whose campaign "lost momentum" after his revelation at the weekend that he took cocaine more than 20 years ago.
Peston continued that Mr Johnson remains "out in front" at present, with many Tory MPs feeling he will "definitely win" the contest.
He added that come the first round of voting, the "gloves will come off" between the candidates, with the race likely to "turn nasty".
The leadership race heated up throughout the day as candidates launched their official campaigns to take over from Theresa May, with many using the opportunity to swipe at frontrunner Boris Johnson's recent tax pledge.
He used his column in The Telegraph to pledge a tax cut for about 3 million people earning £50,000 - a policy that has received criticism.
Mr Johnson's leadership rivals tore into his priorities as the battle for Number 10 intensified.
Michael Gove said: "One thing I will never do as prime minister is to use our tax and benefits system to give the already wealthy another tax cut."
Dominic Raab said he would rather cut taxes for the lowest paid rather than what would be interpreted as "the caricature that you're the party of privilege and you are only in it to help the wealthy".
Matt Hancock said he would reduce tax on working people "when we can afford it".
Andrea Leadsom said it would be "impossible" for Mr Johnson to get his plans through the current Parliament.
If elected leader - and therefore prime minister - Mr Johnson said he would use cash set aside to pay Europe for a no-deal Brexit to finance a move to up the 40% tax threshold to £80,000.
Meanwhile, Mr Gove aimed to draw a line under his cocaine-taking revelations, which many thought would damage his leadership chances, saying: "I'm in it to win it".
How will the next Tory leader be decided on?
When the environment secretary officially launched his bid to be Tory leader he attacked Boris Johnson at least three times in doing so.
Not only did he appear to criticise Mr Johnson's tax pledge, he also sent a message to the former London mayor, saying "don't pull out" the race.
He said: "Mr Johnson, whatever you do, don't pull out, I know you have before, and I know you may not believe in your heart that you can do it."
Mr Gove opened his speech with an explanation of his backstory.
Referring to his adoption at four months old, Mr Gove said: "I remember my mum telling me about my adoption - son, she said, you didn't grow under my heart, you grew in it."
He went on to speak about his controversial decision to back Brexit in 2016, saying he has "led from the front undaunted by criticism and resolute in the need to solve complex issues because that is what our country needs."
Mr Gove said that Brexit was an "unshamedly personal" matter for him, having been one of the leaders of the official Vote Leave campaign in the referendum.
"I made a decision to join the campaign I led from the front and I knew in so doing I would be putting friendships at risk and my family under the spotlight," he said.
"But I did it for one reason. I believed it was the right thing to do at a critical moment in our history."
He would be prepared to delay Brexit beyond October 31 if negotiations with the EU on a new deal were making progress.
He said that if, in those circumstances, the UK was to leave without a deal, it would lead to a Labour government.
"There would be a vote of confidence in the House of Commons that the Government would lose, there would be a general election. We would have Jeremy Corbyn in Downing Street by Christmas," he said.
"So yes, I would be willing to delay for a day, or a week, or whatever is required to get that deal over the line if we were making progress."
The leadership race was triggered on Friday when Theresa May handed in her resignation letter to the backbench 1922 Committee.
While she steps down as party leader, Mrs May will continue as prime minister until the new Conservative leader is chosen through a ballot of party members, likely before the summer recess in a few weeks' time.
In all, 11 Tories have said they plan to run for leader, including Brexit supporter Dominic Raab.
Dominic Raab launches leadership campaign with climate change and energy pitch
Mr Raab, the former Brexit secretary who claimed negotiations with the EU would have gone better had he not been "undermined" in government, said the country needs "stubborn optimism" to succeed.
When asked, during his speech, by ITV News Political Correspondent Paul Brand, what set him apart from the race's frontrunner Boris Johnson, Mr Raab, with a smile on his face, said he wouldn't "speak ill of any of our candidates".
Despite claiming not to criticise the opposition, Mr Raab went on to compare his tax pledges to Mr Johnson's - who has promised to cut taxes on people earning £50,000.
He went on: "Boris is a wonderful campaigner. I think this is a time for change and I think I offer a vision of change for the future, talking about a fair economy.
"My tax cuts are for the very poorest in work and I think we need a generational change of leadership."
He added: "Think about what it's going to be like for the next prime minister, going into those Labour marginal seats - I'd much rather be going there saying that I'm going to cut the taxes of the lowest paid in work than succumbing to what will inevitably, whoever's the prime minister, the caricature of that you're the party of privilege."
He painted himself as "the conviction Brexiteer with a plan" and said the UK's departure from the EU cannot be delivered with "bluff and bluster".
In his keynote speech on Monday, the former Brexit secretary spelled out his desire to break from the EU by October 31 even without a deal if necessary.
"We're up against it and we won't deliver Brexit with bluff and bluster," he told the London event.
"I'm the conviction Brexiteer with the plan, the discipline and the focus to lead us out by the end of October."
The MP, who quit his Cabinet post under Mrs May saying he could not support her deal to take the UK out of Europe, pitched a campaign focusing on climate change and energy.
In his speech, said: "We've got to look to the future. We've got to leave the environment in a better state than we found it."
Foreign Secretary Jeremy Hunt launches leadership campaign backed by Amber Rudd and Penny Mordaunt
Jeremy Hunt's leadership chances received a significant boost after it was announced Work and Pensions Secretary Amber Rudd was supporting him, but a surprise backer was revealed to be Defence Secretary Penny Mordaunt, who addressed crowds before Mr Hunt's speech began.
Mr Hunt used his launch event to stress his credentials as a statesman who can handle the complexities of Brexit.
He said: "Our failure to deliver Brexit has put our country and our party in grave peril.
"The leadership I offer is based on one simple truth: without Brexit there will be no Conservative government and maybe no Conservative Party.
He added: "So delivering Brexit and winning the next election are not different things - they are the same.
"And the person most likely to do that is someone who can negotiate a deal that will pass through Parliament.
"As an entrepreneur and Cabinet minister who has spent his whole life doing negotiations, I am that person."
In what has become a theme of this leadership race, Mr Hunt was asked by ITV News Political Editor Robert Peston if he had ever broken the law.
Mr Hunt responded: "I'm really racking my brain at the moment, but the answer is no."
'My Brexit plan is the only credible option': Matt Hancock launches his leadership campaign
Mr Hancock, while launching his leadership campaign argued the country needs "a leader not just for the next six weeks or six months, but the next six years and more".
Pointing toward Brexit, Mr Hancock, who backed remain in the EU referendum, ruled out proroguing Parliament in order to ensure the UK leaves the EU on October 31.
During his speech in central London, the health secretary said: "My Brexit delivery plan is the only credible plan that can deliver Brexit by the 31st October with the support both of the European Union and the House of Commons - that is just the reality of the situation.
"Some have said 'stick with the current plan', but the current plan has been seen to fail.
"Others say 'let's just run at no-deal', but the brutal truth is we know that no-deal will not get through the House of Commons.
"And then there's this idea from some people that to deliver Brexit we should suspend our parliamentary democracy - that we should prorogue Parliament.
"But that goes against everything that those men who waded onto those beaches fought and died for, and I will not have it."
"We are facing a constitutional crisis. Our new prime minister will preside over a hung Parliament," Mr Hunt will say.
"This extremely serious moment calls for an experienced, serious leader. We need the art of tough negotiation, not the art of empty rhetoric."
Previously, runners had only to get two others to back them - but the rules were changed last week as there were concerns there could be as many as 15 to 20 hopefuls entering the race.
The field of candidates to replace Theresa May is dominated by men, with only two women - Anrea Leadsom and Esther McVey - entering the race.
Esthey McVey launches campaign as protester interrupts
The TV presenter-turned-politician had trouble with her launch event which was interrupted by a protester and suffered technical difficulties, meaning it wasn't streamed live.
Esther McVey, flanked by a portrait of Margaret Thatcher, promised to give public sector workers a pay rise, and boost funding for policing and education.
Speaking at a meeting of the eurosceptic Bruges Group in central London she said: "I want to stand for leader of the greatest political party ever, the Conservative Party.
"My clear agenda is to deliver Brexit on the 31st of October and then we must unite the country, and then unite our party too."
She added: "Britain's public sector workers need a pay rise and our police and our schools desperately need cash. That's what my campaign is about."
Immediately after the launch a heckler, who described himself as a "paid-up member" of the Tory Party, took to the podium to shout: "Excuse me, you are all fake news and these people are fake Conservatives."
The protester, who said his name is Graham Moore, told Paul Brand he’s angry that MPs haven’t delivered Brexit.
Other Tories in the leadership race
Along with the leadership hopefuls who launched their campaigns with official events were other Conservatives who claimed to have gained enough nominations to proceed in the race.
Around five minutes before the deadline, Andrea Leadsom tweeted: "Just handed in my nomination papers - thanks so much to all those supporting! Looking forward to the campaign launch 9.45am tomorrow."
Rory Stewart, who also made it through, described himself as the "anti-Boris" candidate, saying he is the only contender capable of beating the former foreign secretary.
"I think I am the only person who can beat him. We are facing a very, very fundamental choice," he told reporters at Westminster as the nominations were announced.
"That choice is between Boris's Brexit and my Brexit, between somebody who is attempting to out-Farage Farage and somebody like me who believes in the centre ground."
Outside Mark Harper also made it through to the first round.
He tweeted: "Pleased to be officially nominated as a candidate for Leader of the @Conservatives - here with my Proposer @JackieDP and Seconder @SteveDouble. I look forward to setting out to my colleagues why I am."
Former leader of the House of Commons Andrea Leadsom also gained the backing of at least eight MPs as she starred in an ITV News podcast.
Despite no official event on deadline day, Home Secretary Sajid Javid also made it through to the first ballot after he received eight nominations.