Boris Johnson expected to be named Britain's next prime minister

Boris Johnson is expected to be elected leader of Britain's governing Conservative Party and the next prime minister on Tuesday, tasked with following through on his "do or die" pledge to deliver Brexit in just over three months time.

Johnson and his rival, Foreign Secretary Jeremy Hunt, have spent the last month crossing the country seeking to win over the fewer than 200,000 Conservative Party members who will choose Britain's new leader.

The winner will be announced at about 1045 GMT at an event near parliament and will formally take over as prime minister on Wednesday afternoon, succeeding Theresa May, who stepped down over her failure to get parliament to ratify her Brexit deal.

Johnson, a former London mayor who resigned as foreign minister a year ago over May's Brexit plans, is the clear favourite to replace her, with several polls putting him on around 70 percent.

"It's all to play for," Johnson told reporters as he arrived at his office in Westminster.

He will inherit a political crisis over Britain's exit from the European Union, due to take place on Oct. 31. Johnson must persuade the EU to revive talks on a withdrawal deal that it has been adamant cannot be reopened, or else lead Britain into the economic uncertainty of an unmanaged departure.

The only divorce deal on the table has been rejected three times by parliament and many lawmakers - including pro-EU rebels in the Conservative Party - are vowing to block Johnson from trying to take Britain out of the EU without a deal.

He has said he would ramp up preparations for a no-deal to try to force the EU's negotiators to make changes to the accord.

"DO OR DIE"

"We will of course be pushing our plan into action, and getting ready to come out on October 31st, come what may ... do or die," Johnson told TalkRadio last month.

Sterling fell for the third straight day, partly due to concern that the new prime minister will back a no-deal Brexit.

Whoever wins faces the same parliamentary problems that brought down May.

The Conservatives only govern with the support of 10 lawmakers from the Brexit-backing Democratic Unionist Party in Northern Ireland. Even with their backing, the working majority can be counted on one hand.

While some Conservative lawmakers will demand the new leader ensures an EU exit by Oct. 31, a group Johnson has wooed to enhance his leadership prospects, others have hinted that they would be prepared to bring down the government to stop a no-deal Brexit.

The new prime minister will also be acutely aware of the electoral threat posed by Nigel Farage's Brexit Party, which won the most votes and seats in May's European Parliament elections, while there has been a surge in support for the pro-EU Liberal Democrats.

Johnson is not likely to start announcing key ministerial appointments until Wednesday, but his expected victory in the leadership contest is likely to prompt several resignations in his bitterly-divided party.

Two junior ministers have quit over Johnson's willingness to leave the EU without transition arrangements and finance minister Philip Hammond and justice minister David Gauke have both said they plan to resign before they are sacked.

Brexit without a divorce deal - as anti-EU hardliners would like - would abruptly wrench the world's fifth largest economy away from the bloc. Critics say this would undermine global growth, buffet financial markets and weaken London's position as the pre-eminent international financial centre.

"I want him to succeed, I want him to do what he says he wants to do which is leave the European Union with a deal," Gauke told BBC radio, warning that a no-confidence vote in Johnson could result in a government headed by Jeremy Corbyn, the veteran socialist leader of the opposition Labour Party.

"People have to be wary about that," Gauke said.