Britain's main opposition Labour party is "now the political mainstream" and "ready for government", leader Jeremy Corbyn said today following unexpected advances in a June general election.

Labour was "on the threshold of power," Corbyn told the party's annual conference in Brighton, the first since the election in which Conservative Prime Minister Theresa May lost her parliamentary majority.

"We've become a government in waiting," he said, adding that Labour were "ready to build a new and progressive relationship with Europe".

Corbyn has met with significant resistence from Labour MPs over his attempts to move the party to the left since being elected leader in September 2015.

But he defied expectations by winning 30 more seats in June on a manifesto promising nationalisations and a huge increase in public spending.

"A new consensus is emerging from the great economic crash and the years of austerity, when people started to find a political voice for their hopes, for something different and better," Corbyn told delegates.

"This is the real centre of gravity of British politics. We are now the political mainstream."

Corbyn said May's Conservatives, who are riven by infighting over the government's strategy on Brexit, were "hanging on by their fingertips".

But Labour is also divided over Brexit, particularly over whether Britain should continue to have access to the European single market after it leaves the EU and continue to accept free movement of people.

Corbyn offered no details on Labour's position on Brexit in the speech and instead attacked Conservatives for "bungling" Brexit negotiations.

A YouGov poll for The Times published on Wednesday showed Labour on 43 percent compared to the Conservatives on 39 percent.

But the poll of 1,716 people conducted last week showed trust in May as a leader was at 37 percent compared to 29 percent for Corbyn.

In the June 8 election, Labour gained 30 seats and the Conservatives lost their majority.

May has since struck a deal to govern with the help of the 10 MPs from Northern Ireland's Democratic Unionist Party.