|To Be Or Not To Be|
And he did not think "too many people" had come to the UK from inside the EU.
David Cameron said they disagreed on "lots of things" but welcomed Mr Corbyn's backing for EU membership - as Leave campaigners said the Labour leader "does not really mean it".
Making his first major speech of the EU campaign, Mr Corbyn stood by past criticisms of the EU but said Britain had to remain in to fight for social reform.
Read more: EU referendum: Jeremy Corbyn warns of workers' rights 'bonfire' if UK leaves - BBC News