The UK needs to be given concessions to be able to stay in the EU customs union, and must be given political representation, says Gabriel Felbermayr of influential German economics think tank the Centre for International Economics (IFO).

"We still underestimate the loss that the exit of the UK would mean for Europe in general. The biggest asset that the EU has is the size of its single market. This is what matters in international negotiations, when we talk with Beijing, or Washington, or New Delhi. Without the UK, the EU is almost 20% smaller. This is important.