Labour' new leader Jeremy Corbyn, pictured at a pro-refugee rally in London on September 12, 2015, was a co-founder of the Stop the War movement which organised Britain's biggest ever march against the 2003 invasion of Iraq
London (AFP) - Veteran socialist Jeremy Corbyn was elected leader of Britain's Labour opposition on Saturday in a landslide victory that puts an anti-austerity figure at the helm of a major UK party.
The 66-year-old, whose policies have been compared to those of radical leftist Greece's Syriza and Spain's Podemos, won after clinching 59.5 percent of the vote, giving Britain its most left-wing leader in decades among the main parties.
The new Labour chief could divide Britain's biggest opposition party, and he immediately faced shadow cabinet resignations amid warnings from party grandees that Labour could be consigned to electoral oblivion.
In his victory speech, Corbyn slammed Prime Minister David Cameron's centre-right Conservatives for presiding over "grotesque levels of inequality" and for creating "an unfair welfare system".
As the win was announced at a conference centre in London, supporters chanted "Jez We Can!" while centrist figures looked shell-shocked.
Corbyn later thanked his supporters in a nearby pub, where he joined in a rendition of the traditional socialist anthem "The Red Flag".
"It's a fantastic moment for change in Britain," he told reporters as he arrived at the bar.
The veteran member of parliament has said he will oppose Britain joining in air strikes against the Islamic State jihadist group over Syria and has been ambiguous about his stance on an upcoming referendum on Britain's EU membership.
Addressing tens of thousands of people at a pro-refugee rally in London later on Saturday, Corbyn alluded to Cameron's reference to air strikes as part of the solution to the migration crisis.
"Surely our objective ought to be to find peaceful solutions to the problems of this world," said Corbyn, to huge cheers.
As support for anti-austerity parties swells across Europe, Greece's hard-left Syriza welcomed Corbyn's election, saying it represented a "message of hope" and would bolster a "pan-European front" against crippling government spending cuts.
Spain's leftist Podemos leader Pablo Iglesias tweeted that Corbyn's triumph was "a step forward towards a change in Europe for the benefit of the people".
- 'Serious risk' to security -
In a campaign driven by protest groups and trade unions, Corbyn comfortably beat the more centrist Yvette Cooper, Andy Burnham and Liz Kendall -- who all had far stronger support from fellow Labour MPs.
Corbyn electrified Labour's leadership race, which was triggered by the resignation of Ed Miliband after he lost May's general election to Cameron's pro-austerity Conservatives.
Corbyn's chances at the next general election in 2020 are thought to be slim but the Conservative Party was quick to denounce Labour's new direction.
"Labour are now a serious risk to our nation's security, our economy's security and your family's security," said Defence Secretary Michael Fallon.
In a one-sentence statement, Downing Street said Cameron had spoken to Corbyn on the telephone "to congratulate him on becoming the new leader of the opposition".
- Call for party unity -
Corbyn's policies include spending more on public services like schools and hospitals, scrapping nuclear weapons, renationalising the railways and involving Islamist groups Hamas and Hezbollah in Middle East peace talks.
He drew strong support from students who had never voted before as well as from older people disillusioned with Labour since it moved to the centre-ground of British politics under former prime minister Tony Blair in the 1990s.
Corbyn, a bearded, grey-haired vegetarian, crammed in 99 campaign appearances, eschewing soundbites and usually wearing sandals and carrying a cup of tea.
While many Labour MPs praised his personal qualities, several indicated they would not be prepared to serve in the shadow cabinet under his leadership.
Labour health spokesman Jamie Reed even posted his resignation letter on Twitter during Corbyn's victory speech.
Of the 232 Labour MPs, 35 backed him for the leadership, and many of those did so simply to ensure a broader debate within the party.
Former leader Miliband said he hoped Corbyn "reaches out to all parts of the party".
Corbyn won 50 percent of the vote from Labour members, 84 percent from people who paid Â£3 ($4.60, 4.10 euros) to get a vote, and 58 percent among trade unionists.
Meanwhile Tom Watson was elected Labour's deputy leader. The 48-year-old had a big hand in pushing Blair into stepping down in 2007 and is a fierce critic of media baron Rupert Murdoch.
The News Corp mogul said on Twitter: "Hard left Corbyn wins in landslide, goes on TV singing 'Red Flag'. How did Cameron get this lucky? Hope he doesn't slack off."
Blair -- Labour's most electorally successful leader who is now domestically deeply unpopular over the war in Iraq -- warned during the campaign that Corbyn's victory would split the party and lead to electoral oblivion.