Britain's prime minister David Cameron has started a four-month campaign to persuade voters to remain in the European Union ahead of a referendum on 23 June, saying the country will be "stronger, safer and better off" if it stays in the bloc. In a video statement, Cameron said the decision for voters centred on the health of the economy, the fight against terrorism and maintaining influence on the EU.

"This referendum is straightforward. It's about you and your family. Where will you be better off? Where will there be more trade, more jobs and lower prices: in or out? Where will you be safer? Where are terrorists more likely to be tracked down and criminals brought to justice: in or out? Where will our country be stronger? Where will Britain have the biggest influence: in or out?" Cameron said.

He questioned those supporting Britain's exit from the EU, saying the country occupies a special position, wielding influence without being bound by many of the obligations applied to other members of the bloc.

"Some say we could leave and carry on trading with our neighbours. But the countries outside the EU with full access to the single market still have to pay into it, and accept immigrants, and they don't get any say on the rules that affect them. Britain is different. We now have a special status in Europe, the best of both worlds. Access to the world's largest single market but no discrimination because we don't have the euro, and no obligation to bail out euro zone countries," Cameron said.

Brits can move freely inside the EU

He added that Britons retained the freedom to move within the EU and benefited from better security through close cooperation, but could keep itself out of grander European projects.

"We have the right to live, work and retire abroad but no Schengen open borders. We've got co-operation on vital security issues but no European army. And we've got influence over the biggest global issues but no part in a European superstate," Cameron said.

He said there was certainty about a British future inside the EU and that choosing to leave would be "a leap in the dark. I'm not saying Europe is perfect. Far from it. But by staying in, we can continue to reform it. And the point is this. We know what that reformed Europe looks like. No one can say what being out of Europe would look like," Cameron said.

"On what terms would we trade with Europe? What would be the cost? How long would it take to sort it all out? What would happen to jobs and our economy in the mean time? What about our trade with the rest of the world? What about our agreements with other European countries on crime? The times we work together to tackle our biggest threats? What about Britain's clout on the world stage? No one can say. No one knows."