If it seems the EU referendum debate just involves two politicians shouting contradictory statistics at each other - then we are here to help. In this series, we're giving you a break from the politicians and we're going to try to figure out the truth. Bracing concept, isn't it? We'll be looking at some of the big questions - The cost of the EU, lawmaking, regulations and trade. In th secomd of these programmes Tim Harford asks what might happen to migration if we left the EU, and what are the benefits and costs of EU migrants to the UK economy?