The EU has ended centuries of bloodshed between European nations as member states now battle with ideas instead of weapons, Gordon Brown has stated. The former Labour prime minister made the claim during his first speech of the EU referendum campaign.

"You've got to think of the sweep of history here," Brown told an audience at the London School of Economics on Wednesday morning (11 May 2016). "For a thousand years, nations and tribes of Europe were fighting to the finish, murdering and maiming each other.

"There is no century except this one when Europe has been at peace, and where nations – whether it be Germany, France, Spain or the Netherlands, Britain or Germany –were not vying for supremacy.

"What has happened in these last 70 years since the Second World War is not a temporary truce, it is not simply a ceasefire, it is not simply a peace held together by the threat of arms if it breaks down. It is the development and evolution of a new structure of decision-making, where instead of battling with weapons and armaments, people battle with arguments and ideas."

The comments echoed David Cameron's own claim that a Brexit could trigger a conflict on the continent. Brown, who blocked Britain joining the euro currency in 1997 as chancellor, also made a direct plea to Labour-voters. The pro-EU campaigner argued that Brussels has blocked a "race to the bottom" in workers' rights with its labour laws.

"Think of the social chapter in Europe, preventing a race to the bottom, preventing dog-eat-dog competition between European nations with each other," he said. "We have managed to create something better than that. So a customs unions became a common market, then became a single market and is now actually a social market. Underpinning the EU now is the belief that markets need morals."

The intervention coincided with the launch of Vote Leave's battle bus tour with Boris Johnson. Brown said he would be "happy" to debate with the former Mayor of London, and raised doubts about his unionist credentials. "I'm happy to take anybody on these days," he told journalists. "I was part of the Scottish referendum campaign, and I'm not so sure that Boris was on our side on that either."

The former prime minister concluded his speech by urging the UK to become a leading member of the EU. "We should not be fully out and we should not be half-out – we should be fully in. We should recognise that the world has changed since the first referendum [in 1975], and we should be the advocates of cooperation in an interdependent world."

Brexit campaigner and cabinet minister Chris Grayling hit back at Brown's speech by arguing that his EU policies were a "disaster" when he was in office. "He gave away huge amounts of money to the EU when they cut our rebate, he broke his promise to hold a referendum on the Lisbon Treaty and he gave away many new powers to Brussels," Grayling said.

"The EU is undermining our ability to stop multinational companies milking our tax system. We face tens of billions of pounds of liabilities in the next few years because EU judges have ruled in favour of big corporates instead of UK taxpayers."

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