Gordon Brown has expressed fears about what a vote to leave the European Union would say to the world about Britain.
A Brexit win would suggest that Britain is unable to cooperate with its nearest neighbours and would deny young people the chance to make plans, the former prime minister said.
He also urged mothers to vote for Britain to stay in the EU for the sake of their children’s future.
Around 500,000 new jobs can be created by opening up the single market further to British firms, the former premier told the Fabian Society summer conference.
He issued a direct plea to more than nine million Labour voters as well as young people to turn out for the referendum on June 23.
For centuries Britain has engaged with the world, he said, adding: “If we the British then decided we were going to walk away from our nearest neighbours, refuse to cooperate on economic and other matters that are vital to our future, deny young people in our country the chance to plan for the future because we are breaking off links to countries that are nearest to us, what sort of message would we send to the world about what kind of world we are going to build for the future if we could not engage in cooperation with our nearest neighbours?”
Mr Brown, who received a standing ovation after his 45-minute speech, reminded the crowd of what the Labour Party constitution says.
“By the strength of our common endeavours we can achieve more together than ever we could achieve on our own,” he said, adding that this is the message people need to take on board about Europe.
He also made his case to young people – who may not vote “unless we challenge them to do so”.
Mr Brown added: “To mothers who are worried about the prospects for their children in the future and want to know where the jobs will come from, to people who feel that globalisation is a runaway train and it’s out of control and uncontrollable, we’ve got to show that we can manage that in the public interest.”
He concluded his speech by saying: “It matters that we vote to Remain in the European Union to achieve all these aims.”