Britain's parties in leadership tumult after Brexit shock

Britain's two main political parties were in Brexit turmoil on Tuesday as the race to succeed Prime Minister David Cameron began in earnest and opposition leader Jeremy Corbyn faced a no-confidence vote from Labour MPs.

Britain's opposition Labour Party leader Jeremy Corbyn leaves his home in London this morning.

Five days after the shock vote for Britain to leave the EU, the two parties that have dominated Westminster for nearly a century were in almost complete disarray.

Pro-EU finance minister George Osborne, long tipped to succeed Cameron, ruled himself out on Tuesday.

That left former London mayor and "Leave" figurehead Boris Johnson -- but now a bogeyman for many in the "Remain" camp -- tipped as the most likely candidate.

The Conservatives have set a Thursday deadline for nominations, with Home Secretary Theresa May the other frontrunner.

Corbyn defiant

On the opposition side, Corbyn has said he will not stand down and does not have to even if Tuesday's no-confidence vote goes against him since it would then be up to the party's 150,000 members to vote on a new leader if he puts himself forward again.

Over half of Corbyn's shadow cabinet -- the leadership of his party -- have stepped down since Sunday in a coordinated series of resignations against the 67-year-old, who only became leader in September.

Corbyn, a veteran socialist and eurosceptic who voted against EU membership in a 1975 referendum, has come under heavy criticism from pro-EU lawmakers for his lukewarm campaigning in favour of Britain staying in.

Many experts have blamed the strong anti-EU vote in Labour heartlands in northern England on Corbyn.

But Corbyn himself has blamed Conservative austerity measures for creating disenchantment in many working-class areas and said the media had not covered Labour's referendum campaign, focussing instead on rifts within the ruling Conservatives.

Corbyn -- who blasted "internal manoeuvring" within his party -- was defiant on Monday at a rally organised by the grassroots Momentum movement, largely made up of the far-left campaigners who helped get him elected.

"Don't let the media divide us. Don't let the people who wish us ill divide us. Stay together, strong and united for the kind of world we want to live in," he said.

Voting on the no-confidence motion is due to close around 4:00 pm (1500 GMT), with results expected about an hour later.

Boris or Theresa?

The Conservatives are meanwhile scrambling to choose a successor to Cameron, who announced his resignation within hours of the Brexit result last Friday, saying he wanted he or she to be in place by October.

EU leaders said they wanted Britain to move more quickly, and on Monday the Tories said they expect the new leader to be in place by September 2.

A new poll Tuesday put May in the lead with 31 percent, against 24 percent for Johnson.

Nominations for the party leadership open Wednesday, and close Thursday.

If more than two candidates stand, Tory MPs will vote next week to whittle down the field to two nominees, before the new leader is chosen by a postal ballot of party members, who currently number around 150,000.

Critics have questioned whether the "Leave" camp -- and Johnson in particular -- has any idea how to manage the unprecedented situation left by last week's vote.

"He has still to offer anything like a concrete plan on how he would negotiate the post-Brexit future," wrote former BBC political editor Nick Robinson.

He added: "The fallout from the biggest exercise in popular democracy has already been dramatic... It has, though, only just begun.

"The old order has been smashed. It may be a very long time -- not weeks, not months but years -- before the shape of the new order and the answers to all those questions become clear."