The divisions go back to the failure in 2015 of Labour — then led by Ed Miliband — to win the general election, allowing the Conservatives, under David Cameron to take power, albeit with a slim majority. Miliband stood down, paving the way for a leadership race.
There were three front-runners: Andy Burnham, former health spokesman, Yvette Cooper, shadow home secretary and Liz Kendall, shadow minister for care and older people. Then, left-wing firebrand Corbyn joined the race and was seen as a dark horse.
However, because of the voting system, a huge number of people joined the party as supporters and were able to cast a vote. Corbyn won by a landslide — supported by many left-wingers and the unions, who were tired of the party's move to the center ground under Tony Blair and Gordon Brown.
In Corbyn, the party faithful saw a left-winger with strong views against capitalism, who was anti-war and particularly angered by Blair's decision to invade Iraq and was strongly anti-nuclear weapons as well.
Westminster v Grassroots
However, he did not enjoy the support of the majority of the Labour members of parliament. They were angered by Corbyn's lackluster support, during the In-Our referendum on the UK's membership of the EU, for remaining in Europe. He is known to be anti-EU, but towed the party's line, which was to remain.
When the result came through that 52 percent backed leaving the EU, his parliamentary colleagues turned on him and held a vote of no confidence in him, which was won by 172 votes to 40. Corbyn has refused to move, however, saying he has a mandate from the 2015 leadership election, with the backing of grassroots party members and the unions.
Former pensions minister Angela Eagle Monday (July 11) threw her hat in the ring triggering a leadership run-off. However, there is a row over whether Corbyn will automatically be on the ballot paper or whether he requires the nomination of a number of MPs — which he is unlikely to get.
Corbyn has said that, unless he is automatically on the ballot paper against Eagle — and any other who decide to join in — he will sue the party.