British opposition leader Jeremy Corbyn said on Wednesday Labour would vote against a Brexit deal based on Theresa May's proposals, the strongest warning yet to a prime minister whose plan to leave the European Union is hanging by a thread.

On the final day of his party's annual conference, Corbyn sought to show that his party was ready to take over the reins of power, setting out in the most detail yet what he called "a radical plan to rebuild and transform our country" and promising new jobs from a green "revolution".

Corbyn also made a direct bid for the support of those outside the British capital who voted to exit the EU, often in frustration at feeling left behind by a London-based elite, saying Labour was ready to take over the tortured Brexit talks.

Britain is not due another election until 2022, but Labour is already preparing for a snap vote.

Despite her denials, few are ruling out an early election after May's already precarious position was further weakened last week when the EU rebuffed her Brexit proposal, known as "Chequers", which is also unpopular in her Conservative Party.

Corbyn, a veteran eurosceptic who in 1975 voted "No" to Britain's membership of the then-European Community, said Labour respected the outcome of a 2016 referendum when Britons voted to leave the EU, the biggest shift in foreign and trade policy in more than 40 years.

"As it stands, Labour will vote against the Chequers plan or whatever is left of it and oppose leaving the EU with no deal," Corbyn told a packed hall at the conference in the northern English city of Liverpool.

"And it is inconceivable that we should crash out of Europe with no deal - that would be a national disaster. That is why if parliament votes down a Tory deal or the government fails to reach any deal at all we would press for a general election. Failing that, all options are on the table."

Corbyn hoped to steer his annual party meeting away from Brexit, which has divided his party just as it has done May's Conservatives and much of the country. Britain is due to leave the EU on March 29, 2019.

The Labour leader, seeking to paper over his party's divisions, has backed a call to keep open the option of holding a second referendum on staying in the EU despite opposition from some powerful trade unions.

REVOLUTION?

May has said she will press ahead with her Chequers proposals to leave the EU, named after her country residence where an agreement was hashed out with her ministers in July.

But with a working majority of only 13 in the 650-seat parliament and a former junior minister warning that as many as 80 of her own lawmakers could vote against, May could have been hoping to secure some support from the opposition.

Corbyn ruled that out.

He told May in his speech that Labour would back a "sensible deal" with the EU, adding that she if can't reach one she should "make way for a party that can".

Setting out his wider agenda for government, Corbyn took aim at the "greed-is-good, deregulated financial capitalism" that led to the 2008 financial crisis, saying politicians, including in his own party, had failed to make "essential changes to a broken economic system".

"That's why Labour is offering a radical plan to rebuild and transform Britain," he said.

He also pledged to create more than 400,000 skilled "green" jobs nationwide by investing in technologies to cut net carbon emissions by 60 percent by 2030 and to zero by 2050.

Corbyn and his team have peppered their conference with policy announcements, trying to show they are ready for the long term. The green jobs plan would cover two terms in government.

With announcements ranging from handing workers shares in companies to expanding free universal childcare, Labour has wanted to showcase their planning for an early election.

But the Conservative Party, running almost neck and neck with Labour in opinion polls, accused Corbyn's team of making "unfunded" promises.

"This is the 37th unfunded promise Labour have made since the last election," said Claire Perry, minister for energy and clean growth. "Labour's ideas have all failed before and would leave the country struggling with more debt, more waste and ordinary working people paying for it - just like last time."