BRIGHTON, England (Reuters) - Opposition leader Jeremy Corbyn told Prime Minister Theresa May on Wednesday to step aside and make way for the Labour party to lead Britain’s Brexit talks, saying his leftist ideas were now the “political mainstream”.

After taking the stage at his party’s annual conference to a standing ovation and chants of “Oh, Jeremy Corbyn”, the leftist leader, once written off by some lawmakers for driving the party into unelectable territory, said Labour was ready for power.

Corbyn is keen to press home his advantage over May, who is struggling to unite her party over Britain’s negotiations to leave the European Union and to keep her own position. She faces a threat from some in the Conservatives who cannot forgive her for the loss of their parliamentary majority in a June election she called.

“Against all predictions, in June we won the largest increase in the Labour vote since 1945 and achieved Labour’s best vote for a generation. It’s a result which has put the Tories (Conservatives) on notice and Labour on the threshold of power,” Corbyn said in his speech.

“Yes, we didn’t do quite well enough and we remain in opposition for now. But we have become a government-in-waiting. And our message to the country could not be clearer: Labour is ready.”

Labour is closing the gap in opinion polls to stand roughly level with the Conservatives, putting it within sight of winning an election.

The Conservatives have said they have no plans to call a vote anytime before 2022. The party is dependent on the support of the small Northern Irish Democratic Unionist Party (DUP) for a majority in parliament, however.

So far, there is little appetite in the Conservative Party to hold an early election, and no clear frontrunner to replace May. The party’s deal with the DUP, however, could be hurt by a trade spat involving Canadian planemaker Bombardier, Northern Ireland’s largest manufacturing employer.

Most Conservatives do not want to open the way for Corbyn, whose promises to end austerity have won over many voters, particularly the young, and who has focused anger over a deadly fire in west London on what he called a government which sees itself “not as the servant of the people but of global corporations”.

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MAINSTREAM

Corbyn has tapped into discontent in Britain, a wider trend seen across Western Europe where the dominance of traditional parties and their beliefs have been increasingly challenged.

With his aides working on the belief that May will be forced into an early election before Britain leaves the EU in March 2019, the party has started to develop their policies, ready to introduce them swiftly.

“It feels like we’ve won, it feels like we’re there, it feels like we’re in government. The only frustrating thing is we’re not, yet,” said Chris Howes, an 18 year-old party activist from central England.

“But we’re ready whenever the election comes.”

After being discounted for pursuing what his critics said were policies harking back to the 1980s when Labour lost power to the Conservatives, Corbyn said Britain was ready for change and his party was ready to move further along its leftist route.

Adding to his policies on renationalization, ending university tuition fees and increased public spending, he said he would bring in a housing policy to make sure local councils would have to win a ballot of existing tenants and leaseholders before any redevelopment plans could go ahead.

“We need to build a still broader consensus around the priorities we set in the election, making the case for both compassion and collective aspiration,” he said.

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“We are now the political mainstream.”

Turning the tables on May who before the June election said Corbyn would lead a “coalition of chaos” if voted in, Corbyn now said her cabinet of top ministers were the ones who had failed so far to negotiate with the EU as one.

“This rag-tag cabinet spends more time negotiating with each other than they do with the EU. A cliff-edge Brexit is at risk of becoming a reality,” he said.

“That is why Labour has made clear that Britain should stay within the basic terms of the single market and a customs union for a limited transition period.”

Labour has also been divided on the issue of Brexit, however. London Mayor Sadiq Khan, a prominent member of the party, said in a newspaper interview on Tuesday that he would back holding a second referendum on whether to leave the EU, a position the party itself has not suggested so far.

Corbyn told members that if in power, Labour would pursue a “jobs first” Brexit, one that guaranteed unimpeded access to the single market.

“So I have a simple message to the cabinet -- for Britain’s sake pull yourself together, or make way.”