British Prime Minister David Cameron warned Tuesday that a vote to leave the EU in a referendum to be held in less than 48 hours would harm the economy, representing a "huge risk" for jobs and families.

"Above all it is about our economy," he said outside the prime minister's residence in London's Downing Street.

"It will be stronger if we stay. It will be weaker if we leave. And that is a huge risk to Britain, to British families, to British jobs. And it is irreversible. There is no going back," the prime minister said.