Watch the video below, in which Hillary Benn MP, Shadow Foreign Secretary, said:
"In the 1975 European referendum, a majority of the Labour movement voted No. Since then many people, me included, have been on a journey and we will be campaigning to remain in the EU when we make the most important decision about our place in the world for 40 years.
"Why? Because we came to realise that social and employment rights could be secured all across Europe and that they protect workers in the UK by preventing a race to the bottom. We've seen the benefits of being part of the single market in terms of jobs, investment, growth, security and influence in the world. And we understand that by working together we have a better chance of dealing with the the challenges facing our world and of keeping the peace."