Polling has put Jeremy Corbyn in the lead in the Labour leadership race, sparking a rare intervention by former PM Tony Blair urging the party base to reject a shift to the left.
Corbyn, who has been MP for Islington North for more than three decades and was returned this year with a majority of more than 21,000, is known as a champion of left-wing causes.
A socialist, 66-year-old Corbyn is an outspoken supporter of anti-austerity, tax rises on the rich and renationalisation. So what else do we know about the veteran leftist and his views?
Corbyn sparked controversy when he described Palestinian Islamist political and militant organisation Hamas as "friends" in a 2009 interview. Yet speaking to Channel 4 news in July, he said the quote was taken out of context.
When asked to explain this comments, he told Channel 4 News: "I think to bring about a peace process you have to talk to people [with whom] you profoundly disagree. There is not going to any peace process unless there are talks involving Israel, Hezbollah and Hamas."
Corbyn supports a reunified Ireland. Corbyn took on significant criticism when he and Ken Livingstone invited Sinn Féin leader Gerry Adams to speak in London in 1984.
He showed his continued support for a united Ireland when he met with Adams and Martin McGuinness in parliament this week.
Taxes and tuition fees
Last week, Corbyn set out a plan to scrap all tuition fees and restore student maintenance grants. He said the £10bn ($15.6bn) scheme could be funded by taxing the rich – a 7% rise in national insurance for those earning over £50,000 a year and a 2.5% increase in corporation tax
"The UK has shifted from taxing income and wealth to taxing consumption; and from taxing corporations to taxing individuals," he said, as reported by LabourList. "We must ensure that those with the most, pay the most, not just in monetary terms but proportionally too."
Corbyn has long supported the renationalisation of railways and utilities, campaigning for services to be brought back under public control.
Writing for the Morning Star, he said: "Without exception, the majority electricity, gas, water and railway infrastructures of Britain were built through public investment since the end of WWII and were all privatised at knock-down prices for the benefit of greedy asset-strippers by the Thatcher and Major-led Tory governments."
The Islington North MP campaigns for the global abolition of nuclear weapons and is a supporter of the Campaign for Nuclear Disarmament.
"So, some people say to me, are we still worried about Hiroshima," Corbyn wrote on his website.
"My reply is that the weapons were used specifically against civilians and while 'fireworks' compared to what is now available, killed and have killed for the past 59 years. Nuclear weapons have saved no lives, killed thousands and maimed many more and impoverished the poor nations who have them."