Jeremy Corbyn has set out his case for why the United Kingdom should vote to remain in the European Union, in his first intervention of the campaign.
The Labour leader stressed the "socialist case" for remaining in the 28-member bloc.
While acknowledging the shortcomings of the EU, he argued that reform should be made from within, and that the EU has provided workers' rights, as well as environmental protection.
However, members of Leave.EU and Labour GO, a faction of the Labour party that supports leaving the EU, have said that Corbyn has been gagged.
They draw attention to Corbyn's past euroscepticism, arguing he voted to leave the old European Economic Community and Maastricht treaty.
But Corbyn said that "over the years I have continued to be critical of many decisions taken by the EU and I remain critical of its shortcomings - from its lack of democratic accountability to the institutional pressure to deregulate or privatise public services.
"So Europe needs to change. But that change can only come from working with our allies in the EU. It's perfectly possible to be critical and still be convinced we need to remain a member.
"I’ve even had a few differences with the direction the Labour party’s taken over the past few years, but I have been sure that it was right to stay a member, some might say I’ve even managed to do something about changing that direction," he added.
He also argued that the Labour party believes in staying in the EU because it is in the best interest of Britons.
It's created investment, jobs and workers' rights, such as maternity and paternity leave as well as paid holiday, he stressed.
"Collective international action through the EU is clearly going to be vital to meeting these challenges. Britain will be stronger if we co-operate with our neighbours in facing them together," he added.
And Corbyn used the speech to urge people to resist blaming the EU or foreigners for the UK's problems.
Meanwhile, Britain Stronger in Europe and Vote Leave were designated as the official campaigning groups ahead of the referendum. Each are entitled to spend up to £7m.
Corbyn said that the EU was not to blame for the problems in the steel industry, and that the UK should work with the EU to protect the industry.
He said: "There are certainly problems about EU state aid rules, which need reform. But if, as the Leave side argues, it is the EU that is the main problem, how is that Germany, Italy, France and Spain have all done so much better at protecting their steel industries?"
And in the wake of the Panama papers, Corbyn said that the Tory government had not done enough, and Labour would work with its "allies in Europe" to tackle tax avoidance.