The great EU debate: Should Britain vote 'in' or 'out' in Cameron's referendum?
Europe expert Charles Grant, director of the CER, said leaving the EU would weaken the British economy. "Britain would receive less foreign investment - Japanese car-makers, international banks and many others come to the UK because they enjoy full access to the EU's single market," he said.
"Outside the EU, Britain's access would be curbed - unless, like Norway, we agreed to accept all EU regulations without having a vote on them.
"And on the outside, Britain would be excluded from existing and future trade agreements between the EU and other parts of the world.
"Finally, the EU - unlike Britain alone - is big enough to help shape global rules on climate, finance and trade."