Former Business Secretary Lord Mandelson said: "If Britain quit the EU, amongst the losers would be businesses foregoing trade and investment opportunities, their employees whose jobs and workplace rights would be at risk, the police and security agencies who would sacrifice vital collaboration."
"The British people would lose the freedom to travel, live and work as they wish across Europe," he continued.
"In return we would get the dubious satisfaction of standing alone in the world."
More top news
Four kittens have been rescued from a fire by emergency services in California, USA.
A mother died after trying to save her three-year-old son when he fell down a cliff during a family hike.
The Government's Universal Credit reform has "serious" flaws that need resolving before it is rolled out, a new report has said.