Newly-elected Conservative Party leader Boris Johnson became British prime minister on Wednesday after Theresa May left Downing Street.  

"The Queen received in audience The Right Honorable Boris Johnson MP this afternoon and requested him to form a new administration," the royal statement read.

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Profile: Boris Johnson

Johnson closes in on PM dream, but harsh realities await

"I have accepted Queen's invitation to form new government," Johnson said in his first speech outside of Downing Street after becoming British Prime Minister on Wednesday.

"We are going to fulfill the repeated promises of parliament to the people and come out of the EU on October 31, no ifs or buts," Johnson, 55, said after arriving at the premier's official residence, No.10 Downing Street.

In his 13-minute speech, he promised to deliver Brexit by October 31 and said he would strike a new deal with the European Union.

European Council President Donald Tusk in his congratulation letter to Johnson said he was looking forward to discussing cooperation "in detail".

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Irish backstop

One of the issues that prevented May getting a divorce deal through parliament was the Irish "backstop" - an insurance policy designed to prevent the return of a hard border between the Irish Republic and the British province of Northern Ireland.

Johnson said that issue could be dealt with.

"Never mind the backstop. The buck stops here," he said, adding that a new deal could be done that allowed for no border checks. He said the backstop was "anti-democratic".

He added, "We can do a deal without checks at the Irish border," he said. "It is of course vital at the same time that we prepare for the remote possibility that Brussels refuses any further to negotiate and we are forced to come out with no deal."

New deal or no deal

He promised to accelerate preparations for a "no-deal" though he said Britain did not want such an exit.

"It is of course vital at the same time that we prepare for the remote possibility that Brussels refuses any further to negotiate and we are forced to come out with no deal not because we want that outcome – of course not - but because it is only common sense to prepare."

"And don’t forget that in the event of a no-deal outcome we will have that extra lubrication of the 39 billion pounds."

Domestic agenda: 'Once and for all'

Rebuking "gloomsters" and the political class who he said had forgotten the people they should serve, Johnson promised to serve the British people who he said were his government’s true bosses.

"I will tell you something else about my job. It is to be Prime Minister of the whole United Kingdom and that means uniting our country, answering at last the plea of the forgotten people and the left-behind towns," he said.

He set out a domestic ambitious agenda beyond Brexit by pledging to fix the crisis in social care "once and for all".

"We will fix it once and for all with a clear plan we have prepared to give every older person the dignity and security they deserve," he insisted.

Johnson also promised to improve infrastructure, make streets safer through hiring 20,000 new police and "level up" education as well as people's living wage.

He also said to "change the tax rule to provide extra incentive" for investment, speed up UK's biotech and space science sectors and promote the welfare of animals.

Cabinet shuffle: Brexit loyalists

Just hours after arriving in Downing Street, the new Conservative Prime Minister began work with one of the biggest culls of senior government jobs in recent British history, changing all of the main ministers.

With 17 of May's former senior ministers quitting or sacked, most of Johnson's new appointees were Brexit supporters. The nomination includes a quarter of female ministers.

His first Cabinet appointment was Sajid Javid, the son of Pakistani immigrants, who has been moved from the interior ministry to become finance minister.

He replaces Philip Hammond, who quit hours earlier after repeatedly condemning Johnson's "no deal" threats and warning of the dire economic consequences if they are enacted.

Brexit true believer Priti Patel was appointed as home secretary. Dominic Raab will serve as foreign secretary replacing Jeremy Hunt, Johnson's rival in the Tory leadership contest.

Hunt said he was quitting the government although Johnson asked him to take a different ministerial role.

"I would have been honored to carry on my work at the Foreign and Commonwealth Office but understand the need for a new PM to choose his team," Hunt said.

"Now is the time to return to backbenches from where PM will have my full support," Hunt wrote on Twitter.

Stephen Barclay remained as Brexit secretary and Michael Gove, Johnson's Vote Leave alumni who later betrayed Johnson to launch his own prime minister campaign in 2016, was moved to the Cabinet Office. He will be responsible for leading preparations for a possible no-deal Brexit in October.

Noting that "talk is cheap", Paolo von Schirach, president of the Global Policy Institute (GPI), during a Skype interview with CGTN, said Johnson has a very complex job with limited Brexit options.

Although the EU has repeatedly said the deal on the table - the one May unsuccessfully sells to the parliament three times - is the only deal on the table, Johnson, in his first speech as prime minister, said he would have "a new deal, a better deal" from the EU on Brexit or threatened to leave the EU with no deal.

Schirach said that Johnson may be able to make the EU "blink" by threatening a no-deal Brexit as EU wants the thing to be finished as soon as possible, but he also pointed out the EU obviously doesn't want to reward a country that threatens to leave.

He also added that if the UK gets it easy on Brexit terms, this may give other countries the idea to follow, which the EU definitely does not want to see.

The president of the GPI said Johnson would also face difficulties in a parliament where his Conservative Party does not have a majority.

The Labour Party is becoming increasingly popular, Schirach noted, adding that they are waiting for a chance to force Johnson to call a snap election, which Labour believe they can win.

(With input from agencies)