The man is a moonbat. He is farther to the left by far than Bernie Sanders. He has expressed sympathy with the IRA, Hamas and Hezbollah. He wants to bring Britain back to the days before Thatcher, when British industry was mostly nationalized and taxes were through the roof. He wants the trade unions to dictate economic policy. He is also a republican (anti-monarchist) in a country where The Queen enjoys a near 80% approval rating.
His election as the head of the Labour Party means he is now the head of Her Majestys Loyal Opposition. If Labour were to win a general election he would presumably be the the next Prime Minister. But he is such a wackjob that most of the shadow cabinet (Labours opposition ministers) just resigned enmasse. He has been attacked directly by almost all of Labours former ministers and the last two Labour Prime Ministers, Gordon Brown and Tony Blair.
Britain's Tories are to the left of Bernie Sanders.