Labour leader, Jeremy Corbyn | Carl Court/Getty Images Jeremy Corbyn: UK should stay in EU ‘warts and all’ The Labour leader has a history of Euroskepticism and remains critical of the bloc’s ‘shortcomings.’

Jeremy Corbyn said the Labour party "overwhelmingly" backs the U.K. staying in the EU, despite the need for reform, in his first major intervention in the Brexit referendum debate Thursday.

The Labour Party's official position is that Britain should remain in the bloc, but Corbyn has previously been critical of the EU and initially refused to rule out campaigning to leave when he was elected leader of the opposition party last year.

Although he has since come down in favor of the In campaign, the Out campaign group Leave.EU has accused the Labour leader's team of attempting to whitewash his Euroskeptic past.

In an attempt to address his past views on Europe and the fact he voted No to the U.K.'s membership of the forerunner to the EU in a 1975 referendum, the Labour leader said the bloc was a smaller, purely market-driven arrangement at that time.

"Over the years I have continued to be critical of many decisions taken by the EU and I remain critical of its shortcomings," he said at the University of London’s Senate House.

"Labour is convinced that a vote to remain is in the best interests of the people of this country," Corbyn said, adding that "you cannot build a better world unless you engage with the world, build allies and deliver change. The EU, warts and all, has proved itself to be a crucial international framework to do that."

"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," he added.

Corbyn said that it was sometimes easier to blame the EU for problems that were actually caused by decisions taken at home. He used the speech to attack the Conservative government's approach to a range of issues, including the response to Tata Steel's decision to close its U.K. operations and the handling of what he called the "tax avoidance industry."

"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?"

"It is not the EU that is the problem," Corbyn said, but the Conservative government in the U.K., "that doesn’t recognize the strategic importance of steel" for the country's economy.

The Labour leader also attacked Prime Minister David Cameron's response to tax evasion. "The most telling revelation about our prime minister … has not been about his own tax affairs … but that in 2013 he personally intervened with the European Commission president to undermine an EU drive to reveal the beneficiaries of offshore trusts," Corbyn said.

The speech comes as a YouGov poll for the Times shows Cameron is less trusted on the referendum than the Labour leader. Cameron’s ratings have fallen eight points since February to 21 percent, while Corbyn rose two points to 28 percent.

YouGov shows the June 23 referendum remains a tight contest with 39 per cent supporting In and 39 percent backing Out; 17 percent were undecided and 5 percent said that they would not vote.