LONDON (AP) — Former British Prime Minister Gordon Brown made an impassioned call Monday for Labour Party supporters to vote to stay in the European Union, amid nervousness in the "remain" camp that it is losing momentum ahead of next week's referendum.
Brown, who governed from 2007 to 2010, said Britain should "lead in Europe" and not leave it.
Polls suggest the June 23 vote on whether to leave the 28-nation bloc could go either way. The "remain" side has stressed the economic uncertainty that would be triggered by quitting, while the "leave" campaign has focused on unease about the large scale of immigration from other EU countries — an approach polls suggest may be reaping rewards.
Brown conceded that globalization and rapid change had made many people anxious and left behind. But he argued that Britain needed to work with its neighbors, not walk away from them.
"The European Union is not the cause of the problem," he said. "If you can get cooperation working, the European Union can be part of the solution to the problem."
Brown's speech is considered significant because his last-minute intervention during the 2014 Scottish independence referendum is credited with bolstering support for remaining part of the United Kingdom.
Labour leaders are increasingly worried that many of their working-class supporters plan to vote "leave," or are confused about where their party stands. Labour leader Jeremy Corbyn has long criticized the EU, and some Labour members feel Corbyn has not made a strong case for staying in the bloc.
With just 10 days to go until the vote, other senior Labour figures are stepping up their campaigning.
Labour's foreign affairs spokesman, Hilary Benn, said in a speech Monday that Britain has "always looked beyond our own shores and engaged with the wider world," and argued that leaving the EU "would make us a poorer Britain. A lesser Britain. A less influential Britain."
European Council President Donald Tusk delivered an even starker warning, saying a British exit could start the unraveling of the political system that had dominated Europe for much of the past century.
Tusk told German daily Bild that Brexit "could in fact be the start of the process of destruction of not only the EU but also of the Western political civilization."
"Not only economic implications will be negative for the U.K., but first and foremost geopolitical," he said. "Do you know why these consequences are so dangerous? Because in the long-term they are completely unpredictable."
He said enemies of the EU "will open a bottle of champagne" if Britain leaves.
"Leave" campaigners have accused pro-EU forces of engaging in "Project fear" because of their claims Brexit would cause economic and political turmoil.
Former London Mayor Boris Johnson, a leader of the "leave" campaign, said his opponents were "rattled."
"You can tell that they are panicking because they are resorting to more and more scare stories, more and more misery, more and more discussion of the end of civilization," he said.
Leave campaigners were accused of using scare tactics themselves after the Leave.EU group tweeted a poster claiming that Britain faces "an Orlando-style atrocity" if it stays in the bloc.
The tweet was deleted after drawing criticism from "remain" campaigners. Equalities Minister Nicky Morgan said linking the referendum to the shooting attack in which 50 people died was "shameful."
Telecoms giant BT became the latest company to take sides Monday, sending a letter to 80,000 staff urging a "remain" vote. The letter said "the majority of businesses — large, medium and small — believe we are better off staying in."
"Virtually all major independent experts believe leaving the EU would result in an economic downturn, one from which it may take several years to recover," said the letter, signed by chairman Mike Rake, chief executive Gavin Patterson and leaders of two major unions at BT.
Many large private-sector employers have said they want Britain to stay in the EU, citing access to the bloc's single market of 500 million people. Small firms are more divided, with some saying they would like to be free from EU regulation.
Raf Casert in Brussels and Geir Moulson in Berlin contributed to this report.