Corbyn comes from the socialist left-wing of the Labour Party and has long been seen as a lukewarm supporter of the 28-nation bloc. In 1975, he voted against joining what was then the European Economic Community.
In a speech today, Corbyn said the EU was not democratic enough and too eager to promote free-market policies at the expense of workers. But, he said global challenges like tax evasion, cybercrime, migrant crises and terrorism all required coordinated international actions to fight them, making "the EU, warts and all" an important vehicle.