Jeremy Corbyn campaigned to take Britain out of the bloc in the 1975 vote but has since come to believe that the benefits outweigh the costs of EU membership

Jeremy Corbyn will tell of his “personal journey” tomorrow from opposing to supporting membership of the EU.

In his first significant intervention in the referendum campaign, the Labour leader will acknowledge that he campaigned to take Britain out of the bloc in the 1975 vote but will say that he has since come to believe that the benefits outweigh the costs of EU membership.

Although he will frame his support in terms of the role of the EU in protecting workers’ rights and holding multinational companies to account, sources said that he would be unambiguous in calling for a vote to remain.

David Cameron has grown concerned about Labour’s ability to motivate its voters to turn out in favour of EU membership on June 23.