Producer - CNN UK Election Brexit

When Margaret Thatcher took her country into the single market, the UK was central to Europe's nascent union. Fast forward a quarter of a century, and five general elections, with two out of the four main parties offering the electorate a referendum on membership, the EU is now central to the fight for the key to Number 10. So how crucial is it for Britain to be part of the club? And what are the costs and benefits of leaving.