Jeremy Corbyn was re-elected leader of Britain's opposition Labour Party on Saturday, ending a "coup" attempt by more moderate lawmakers who say his left-wing agenda can never deliver victory at the polls.

He saw off challenger Owen Smith with 61.8 per cent of more than half a million votes cast in the contest.

​Mr Corbyn thanked voters for their "trust and support" and told the defeated challenger they were "part of the same Labour family".

The veteran campaigner's triumph by 313,209 to 193,229 votes cements his authority over the deeply divided party and will fuel his drive to turn Labour further to the left - a move many of his colleagues say will see them out of power and allow the ruling Conservatives free rein to set Britain's divorce from the European Union.

Jeremy Corbyn's tally was more than 60,000 higher than the 251,417, or 59.5 per cent, he secured in 2015.

He called on lawmakers and members at the party's annual conference in the northwestern city of Liverpool to come together to fight the Conservatives and bring "real change" to Britain.

"Elections are passionate and often partisan affairs, things are sometimes said in the heat of the debate ... which we sometimes later come to regret. But always remember in our party we have much more in common than that which divides us," he said to roars from the crowd of mainly his supporters.

"Let's wipe that slate clean and get on with the work we have got to do as a party together," he said, moving to ease fears that his re-election will widen the divide between the Labour Party's left and right wings and that he may trigger moves to force centrist lawmakers from the party. 

Owen Smith took 38.2 per cent of the 506,438 votes cast out of a total electorate of 654,006.

​Mr Corbyn's victory marks the next phase in a battle for control of the Labour Party.

In power for 13 years until 2010, Labour was dealt a crushing blow by the Conservatives five years later after they cast doubt on whether the party's left-wing policies would protect the economy.

The ruling party, under new Prime Minister Theresa May, still leads by seven percentage points in opinion polls and looks set to plot Britain's exit from the EU largely unopposed.

Election victory

Jeremy Corbyn told the conference his anti-austerity policies had attracted thousands to Labour, helping to almost treble its membership to make it western Europe's largest, and he was ready to lead a more democratic party to election victory in 2020.

But he faces an uphill battle to win over those who voted Labour at the last election but then supported Britain's exit from the EU, after a YouGov poll showed more than half of them have now abandoned Labour.

He also has to convince many Labour members of parliament, some of whom decided not to attend the annual conference, that his left-wing policies, such as renationalisation and campaigning against nuclear weapons, can have broad appeal.

"The words are conciliatory but we need to have practical ways to put things back together and that is what we will wait to see," one senior Labour member of parliament, who declined to be named, said after the result.

Mr Corbyn, 67, attracts a devoted following, but his election to leader last year on a wave of enthusiasm for change also unleashed a backlash against centrist lawmakers where personal attacks, allegations of anti-Semitism and abuse left little room for debate over policy.

Several in the party who once supported his candidacy as a chance to harness a growing disaffection for 'establishment politics' across Europe now rue the day they backed him.

But Mr Corbyn tried to smooth over these divisions, citing his responsibility as Labour leader to unite the party.

"It is also the responsibility of the whole party ... to work together and respect the democratic choice that has been made," he said in his speech.

Centrist lawmakers say they now need to take stock, with some pushing to regain some control of the party machinery and boost groups promoting more centre-left policies.

"It is an understatement to say that this is not the result that many of us wanted but all of us have now got to make an individual decision about how best to serve the Labour Party and how best to make the opposition effective," Labour member of parliament John Woodcock said.

Gareth Thomas, who nominated Jeremy Corbyn for last year's leadership contest only to vote for a more centrist candidate, said: "Labour will now have to unite to focus our attack on Theresa May's Tory (Conservative) Party."

But for Mr Corbyn's supporters, his re-election gives them what some describe as their one chance to make Labour a socialist party.

"This is a fantastic result," Jon Lansman, head of a pro-Corbyn campaign group, said. "What a great base for Labour to get back into government to rebuild and transform Britain." 

Reuters, AAP