Factbox- No easy options as UK seeks new migration rules for Brexit

By Laura Gardner Cuesta LONDON (Reuters) - One of the toughest choices facing Britain as it prepares to leave the European Union is what system it will use to govern immigration from the bloc. Prime Minister Theresa May has said she will heed the message from voters about the need to control the number of workers coming from the EU, but she also wants to secure the best deal possible for Britain's economy. Below is a summary of options for Britain's immigration system once it leaves the EU.