LONDON (Reuters) - Britain could have a new prime minister by early September, the ruling Conservative Party said on Monday, after David Cameron started laying the groundwork for his successor to trigger the country’s exit from the European Union.

Britain's Prime Minister David Cameron speaks after Britain voted to leave the European Union, outside Number 10 Downing Street in London, Britain June 24, 2016. REUTERS/Stefan Wermuth

The government is under pressure to fill a vacuum left when Cameron announced he would resign by October after Britain ignored his advice and voted to leave the 28-member bloc in last week’s referendum.

Triggering a leadership battle that could draw in some of his closest advisers, Cameron urged ministers to work together in the meantime.

One of Cameron’s allies, Chancellor George Osborne, ruled himself out of the leadership race, but British media said other cabinet colleagues were poised to enter.

Cameron also formed a separate unit, staffed by public servants, to help advise Britain on its departure and its options for a future outside the EU.

“Although leaving the EU was not the path I recommended, I am the first to praise our incredible strengths as a country,” Cameron told parliament.

“As we proceed with implementing this decision and facing the challenges that it will undoubtedly bring, I believe we should hold fast to a vision of Britain that wants to be respected abroad, tolerant at home, engaged in the world.”

Asked about the possibility of a second EU referendum, Cameron said the result of Thursday’s vote must be accepted.

Graham Brady, chair of the “1922 Committee” of Conservative MPs, which sets the party’s ground rules in parliament, said the group had recommended that the leadership contest should begin next week and conclude no later than Sept. 2.

That recommendation will almost certainly be passed.

“Both the Conservatives and the country more generally really want certainty. We would like a resolution and we think it would be a good thing to conclude this process as soon as we practicably can,” Brady told Sky News.

He said there should be no new parliamentary election before Britain had negotiated the terms of its exit from the EU.

Several Conservative MPs have urged leadership candidates to try to broker a deal quickly to make sure that any campaign is as painless as possible, and to avoid deepening divisions exposed during the referendum campaign.

“A leadership contest now is not in the interests of our country,” said Justine Greening, international development minister. “It will mean our party focuses inward at the very time our country most needs us to focus outward.”

JOCKEYING FOR POSITION

Osborne, who was once widely regarded as a front-runner to succeed Cameron, said his fierce advocacy for Britain staying part of the EU meant he was no longer a suitable candidate for the highest office.

“I believed in this cause and fought hard for it. So it is clear that while I completely accept the result, I am not the person to provide the unity my party needs,” Osborne said in an article published by the Times newspaper.

Work and pensions Secretary Stephen Crabb is considering a bid to succeed Cameron, Sky News reported, citing sources. He is canvassing Conservative MPs for support along with Business Secretary Sajid Javid, who is seeking to become the Chancellor, Sky said.

The editor of the Spectator magazine tweeted that Health Secretary Jeremy Hunt was also “highly likely” to launch a leadership bid.

But all eyes are on former London mayor Boris Johnson, the most prominent of the “Leave” campaigners and now bookmakers’ favourite to succeed Cameron.

But not all party members back him and many are pressing for “Anyone But Boris”, seeing his decision to back the Leave campaign as a betrayal of his former ally Cameron, according to media reports.

A YouGov opinion poll on Monday showed Home Secretary Theresa May scored better than Johnson on who would make the best prime minister, among both the general public and Conservative voters.

Cameron’s spokesman said the prime minister would not endorse any candidate to succeed him.

Instead, Cameron urged unity both in government and in the country and announced he had set up an advisory unit to help manage Britain’s departure from the European Union and to make sure his successor has all the information necessary to decide the country’s future.

“Clearly this will be the most complex and most important task that the British civil service has undertaken in decades. So the new unit will sit at the heart of government and be led by and staffed by the best and brightest from across our civil service,” Cameron said.

For now, the priority was working together on government business, which some critics say has been all but put on hold since campaigning for the referendum began in February, and reassuring the many migrants who fear their status may change.

Cameron told parliament he would not put up with intolerance, after reports that migrants, particularly those from Poland, had been told by some Britons to “go home” since the referendum.

“Let’s remember these people have come here and made a wonderful contribution to our country. And we will not stand for hate crime or these kinds of attacks,” he said. “They must be stamped out.”