Theresa May will take over the job of British prime minister from David Cameron on Wednesday and form a government with the monumental tasks of extricating Britain from the European Union and uniting a fractured nation.

May, who has been interior minister for six years and is seen by her supporters as a safe pair of hands to steer the country through the disruptive Brexit process, will become Britain's second woman prime minister, after Margaret Thatcher.

Britain's decision to leave has rocked the bloc it joined 43 years ago, and thrown decades of European integration into reverse.

Cameron, who led the "Remain" campaign, announced the morning after the June 23 referendum that he would stand down, triggering a leadership contest in the ruling Conservative Party.

The contest had been due to last until September but ended unexpectedly on Monday when junior energy minister Andrea Leadsom, May's last rival candidate after others were eliminated, abruptly pulled out.

After taking part in his last weekly session of Prime Minister's Questions (PMQs) in parliament's House of Commons at lunchtime, Cameron will make his way to Buckingham Palace to tender his resignation to Queen Elizabeth.

May will then enter Number 10 Downing Street as prime minister before the end of the day.

The shocks of the referendum result, Cameron's resignation, and disarray in the main opposition Labour Party have plunged Britain into its deepest political crisis in modern times.

Apart from the task of executing Brexit, May must try to unite a divided party and a nation in which many, on the evidence of the referendum, feel angry with the political elite and left behind by the forces of globalization.

She is expected to immediately start putting together a new cabinet, a complex political balancing act in which she will try to satisfy opposing camps in her party.

Before the referendum, May had campaigned for Britain to remain in the EU, albeit in a low-key fashion. Since the vote, she has repeatedly said that "Brexit means Brexit" and her backers say she is determined to make the exit a success.

"Of course Theresa is going to want to make sure she's got a balanced ticket that represents the views of different parts of the party," cabinet minister Chris Grayling, who campaigned for Brexit and managed May's leadership campaign, told BBC radio.


May has said she plans to set up a new government department to lead the process of quitting the EU which would be headed by someone who had campaigned for Brexit.

"That's very sensible. It will ensure confidence among those in the party who did campaign to leave that they have a champion who believes in what they campaigned for," Grayling added.

Financial markets, which had been extremely volatile since the referendum, reacted positively to news on Monday that May would become prime minister earlier than expected, with sterling making strong gains against the dollar and the euro.

Despite pressure from other EU capitals to quickly start negotiating the terms of Britain's exit, May has said she would not be rushed into it.

She is unlikely to trigger Article 50 of the EU's Lisbon Treaty - which will formally launch the process of separation and start the clock ticking on a two-year countdown to Britain's actual departure - until next year.

She is expected to promote women ministers to several senior roles, and Cameron's long-serving finance minister George Osborne could lose his job, according to media reports.

Prime Minister's Questions is usually a rowdy event, involving combative exchanges between Cameron and the leader of the main opposition Labour Party while lawmakers from both parties boo and cheer.

But with Cameron on his last day in the job and Labour mired in deep crisis, the atmosphere at this PMQs is likely to be very unusual.

After months of simmering discontent among Labour lawmakers with party leader Jeremy Corbyn, the conflict exploded into the open after the referendum when the vast majority of the lawmakers rejected his leadership, accusing him of failing to campaign vigorously enough for a Remain vote.

Corbyn has clung to his job, citing support from the party grassroots members, and the 116-year-old party is now locked in a bitter power tussle that risks destroying it.

Former minister Angela Eagle launched a leadership bid against him on Monday, and on Wednesday fellow Labour lawmaker Owen Smith also threw his hat in the ring.