Leaving the European Union would set back the cause of fairness and social justice in Britain for decades to come, Ed Miliband has warned.

In a direct pitch to the nine million people who voted Labour at the last general election, the former party leader said the real agenda of the Out campaigners was a direct route to “a more unequal, unfair, unjust Britain”.

Speaking in Sheffield, Mr Miliband that while Leave supporters may “pose as the friends of working people”, most were nothing of the kind.

His intervention comes amid concerns among Remain campaigners that they are encountering significant hostility to the EU on the doorstep in traditional Labour areas.

“Leaving the European Union is a choice that would set back the cause of fairness and social justice for decades to come,” Mr Miliband said.

“And indeed the real agenda of most of those who would Leave is a direct route to a more unequal, unfair, unjust Britain.

“The vast majority of those who would Leave are not trying to build a fairer, more just Britain, as Labour voters understand it.

“They want a race to the bottom in taxes and regulations, a recipe for a Britain that cannot work for working people.”

He pointed to former work and pensions secretary Iain Duncan Smith who had praised the UK’s opt out from the social chapter denying workers’ rights, Ukip leader Nigel Farage, who had opposed raising the minimum wage while questioning women’s rights, and former chancellor Lord Lawson who had dismissed climate change as “mumbo jumbo”.

“They are against regulation wherever it comes from, sceptical about workers’ rights wherever they come from, dubious about laws on the environment wherever they come from,” he said.

“Those who would have us Leave the EU may pose as friends of working people, but the vast majority are nothing of the kind.

“They believe low regulation and low taxes are the way to succeed, whatever the consequences for social justice.”