EU chief negotiator for Brexit Michel Barnier says the UK could face 'consequences' if it chooses to diverge in the future as Brexit negotiation talks enter their final hours. Britain left the European Union on January 31 and will leave the EU single market on December 31 at midnight, with or without a follow-on accord. Without a trade deal, cross-Channel trade will be conducted on basic WTO rules and 47 years of economic integration will be disrupted by tariffs on goods.