On Sunday, Simon Coveney warned against the UK against pursuing a no-deal Brexit, adding that it would "fundamentally disrupt the all-Ireland economy".

He also said the Irish border backstop could not be removed from the current Brexit withdrawal deal - an idea suggested by Mr Johnson.

Need a refresher course on the new prime minister? Check out this video...

Incoming European Commission President Ursula von der Leyen has also issued her congratulations to Boris Johnson.

She is due to take over from Jean-Claude Juncker as head of the EU executive branch a day after the new Brexit deadline of 31 October.

Speaking to reporters, she said she looked forward to having a "good working relationship" with the new UK PM.

There were "many different and difficult issues to tackle", she added.

Chancellor Philip Hammond - who said he would resign if Mr Johnson was elected Tory leader - has tweeted his support for the new PM.

Mr Hammond has vowed to do anything he can to stop a no deal, but suggests Mr Johnson will have his support unless and until he chooses to go down that road...

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Conservative MP and Boris Johnson supporter Robert Jenrick says "this is a fantastic result for Boris Johnson" and he now has a "huge mandate".

"Most people in the country now want him to succeed," the MP says, insisting: "It is not Boris' policy to aim for a no-deal Brexit."

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Tory Brexiteer Steve Baker has told reporters he is "absolutely confident" Mr Johnson will deliver on his promise to leave the EU.

He said: "Boris Johnson wants to be a great Conservative prime minister - a man remembered by history - and I believe he will be justly remembered by history because he'll do the things which he's been saying, take us out of the European Union on time and make this a country which Conservative voters can be proud of."

And the Wycombe MP added: "Although obviously many, many Tory MPs worked together to deliver this result. I'm very pleased that Eurosceptics have united to back Boris."

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Theresa May is on her way out as the UK's leader but what does it mean for the country? Read more on the biggest job in the land.

Italian interior minister and leader of the right wing Lega party Matteo Salvini has tweeted: "Good job #BorisJohnson.

"The fact that on the left they depict him as 'more dangerous than the Lega' makes me like him even more."

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Speaking to reporters, leadership runner-up Jeremy Hunt says he is "very disappointed" to have lost but is proud of the campaign he ran.

"This was always going to be uphill for us, because I was someone who voted Remain," he says.

"I think lots of Conservative Party members felt that this was a moment when you just had to have someone who voted for Brexit.

"In retrospect, that was a hurdle we were never able to overcome."

Asked whether he will serve in Mr Johnson's cabinet, he replies: “These are all discussions that will happen over the next few days.

"I am delighted for the country that Boris has become prime minister, I think he’ll be a great prime minister."

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Brexit Party leader Nigel Farage says he wishes Boris Johnson well in his pledge to take the UK out of the EU by 31 October, adding: "It is 'do or die' not just for Brexit, but for the future of the Conservative Party too."

Richard Tice, chairman and one of The Brexit Party's 29 MEPs, says the new PM has "just 100 days to deliver".

“Boris is not well known for honouring his word on Brexit, since he voted for the terrible withdrawal agreement after calling it vassalage," he adds.

“We are the only party that can be trusted to deliver on Brexit.”

Ivanka Trump - daughter of, and adviser to, the US president - has tweeted Mr Johnson to congratulate him, but can you spot the typo? She later deleted that tweet and posted a corrected version.

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Former Education Secretary Justine Greening congratulates Boris Johnson on winning, and says the Conservative Party are "all pleased" that the contest is over.

She says he needs to come to Parliament on Thursday "and set out his policies". She urges him to set aside a social mobility emergency budget.

Ms Greening adds that no deal would be "hugely damaging" for the UK, but insists she is not thinking of joining the Liberal Democrats.

Rory Stewart, who was among the early challengers for the Tory leadership, implies on Twitter that he is delivering on his promise to resign following Mr Johnson's victory.

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CBI director-general Dame Carolyn Fairbairn said Mr Johnson had "no time to waste" in his first 100 days and she warned him not to "underestimate the benefits" of a good Brexit deal.

She said: "Many congratulations to Boris Johnson. British business shares your optimism for the UK. Let's work together to get our economy back on track and working for communities everywhere.

"Business needs three things in the first 100 days: a Brexit deal that unlocks confidence; clear signals the UK is open for business; and a truly pro-enterprise vision for our country.

"On Brexit, the new prime minister must not underestimate the benefits of a good deal.

"It will unlock new investment and confidence in factories and boardrooms across the country. Business will back you across Europe to help get there.

"Early signals back home also matter. From a new immigration system to green-lighting major infrastructure, there is no time to waste."

While those inside the Queen Elizabeth II centre in London showed their support for Mr Johnson, there was some dissent outside.

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The value of the pound was almost unchanged by news that Prime Minister Theresa May will be succeeded by Boris Johnson tomorrow, after he was named Tory leader this afternoon.

Michael Brown, an analyst at Caxton FX, said the widely-expected Johnson victory had been priced in by currency markets.

"Focus will quickly switch to the next steps - namely cabinet appointments and the Brexit plan," he said.

"The latter will be of more importance for markets, with sterling set to remain under pressure should Boris continue his ‘do or die’ Halloween Brexit stance.”