LONDON: Britain's incoming prime minister Boris Johnson faces an overflowing inbox when he takes office on Wednesday (Jul 24) - delivering Brexit, building a relationship with Donald Trump, deciding what to do about Iran and governing without a majority in parliament.
Johnson, a Brexiteer who has promised to lead Britain out of the European Union with or without a deal by the end of October, was named as the replacement for Prime Minister Theresa May on Tuesday after sweeping to victory in a leadership contest.
Below are the most urgent tasks he will have to tackle:
To deliver Brexit, one of the most divisive policies in decades, Johnson will have to show he can win votes in parliament and govern after three years of political crisis.
The opposition Labour Party is likely to test his ability to govern by calling a vote of no confidence in the 650-seat parliament - although that is not expected to happen before the summer break starts at the end of Thursday's business. Parliament resumes on Sep 3.
On its own, the ruling Conservative Party does not have the majority needed for the new prime minister to survive such a vote, relying under May on the support of 10 allied Democratic Unionist Party (DUP) lawmakers to govern.
Even if the DUP backed the new prime minister in a confidence vote, a handful of Conservative lawmakers have threatened to vote against their own party if Britain looks set for a no-deal Brexit.
Failure to clear this first hurdle would collapse the government and could trigger a general election.
Johnson wants to renegotiate a new deal with the EU, ditching large parts of the accord May struck with Brussels last year, which was rejected by parliament three times.
The EU has repeatedly said it will not renegotiate the legally binding part of that deal, the Withdrawal Agreement which sets out a transition period to smooth Britain's exit.
The problem for Johnson is that the withdrawal agreement contains the most contentious part of the exit deal - an insurance policy to prevent border controls between EU member Ireland and British province Northern Ireland.
EU negotiators are ready to explore several options with the new prime minister, but these fall well short of what Johnson says he wants.
He wants to ditch the so-called backstop; the EU says it has to stay.
If Britain cannot negotiate a new deal, or parliament rejects whatever Johnson brings back from Brussels, the country will be headed for an unmanaged exit from the EU - a so-called no-deal Brexit - on Oct 31.
Johnson says he has to make sure Britain is fully prepared for such an outcome because it is an important negotiating tool and he cannot rule out that it may happen.
Britain had conducted substantial work toward preparing for no-deal ahead of the original Brexit deadline of Mar 29, but as the date approached many expressed concern that those preparations were incomplete and had stagnated.
TRUMP AND THE UNITED STATES
Johnson will need a good relationship with the United States, Britain's closest military ally and a major export market, to help mitigate any impact of stepping away from the EU - its biggest trading partner.
Trump tweeted his congratulations to Johnson shortly after the results of the leadership contest. "He will be great!" Trump said.
But relations between Britain and the United States have suffered in recent weeks after the leak of confidential memos from the British ambassador to Washington which reportedly described Donald Trump's administration as inept.
How Johnson moves on from the spat - which saw Trump respond angrily and the ambassador resign - could set the tone for transatlantic ties during a critical period for Britain.
Both sides say they want to agree a swift and comprehensive free trade agreement after Britain leaves the EU, but political will is likely to determine how quickly that can be done.
IRAN AND CHINA
The United States and European allies are pulling in different directions over the best approach to Iran's nuclear programme, leaving Britain with a difficult choice about who to align with.
Iranian Revolutionary Guards seized the British-flagged tanker Stena Impero in the Strait of Hormuz on Friday, in apparent retaliation for the British capture of an Iranian tanker two weeks earlier.
Allies are watching closely to see whether the new British leader will move towards the United States and away from the EU over Iran policy.
Johnson will also have to decide what role Chinese technology firm Huawei will be given in British communications infrastructure, with Trump warning that the security risks are high and could endanger intelligence ties.
That decision could also set the course of relations with China, one of Britain's top targets when it comes to building stronger trading ties outside the EU.
While Johnson's first test will be to deliver Brexit, he will also have to craft a viable long-term vision of post-Brexit Britain that can win over voters, investors and international allies.
Ultimately, the new leader will have to decide what sort of economy the United Kingdom wants and how it will pitch that to the world while making a choice between aligning with either European or American regulations.