The British government seems to have four red lines. It wants to stop free movement of labour; to be allowed to pursue an independent trade policy; not to contribute to the EU Budget; and to break away from legal oversight by the European Court of Justice. (All of these can be summed up by the slogan "taking back control"). The EU's sole red line seems to be that Britain cannot benefit from "cherry picking"
Trade-offs: Brexit means...a lot of complex trade decisions | The Economist
If you give notice to your landlord or your employer, you trigger a process which, if you don’t do anything else, will leave you homeless or jobless after a given period. Furthermore, even if you do take some action, the decision is still partly in the hands of others. You need to find a house you like and a landlord that will let to you or a job you like and an employer that will have you. For this reason, most people don’t give notice to their landlords without having another home to go to or notice to their employers without having another job lined up. The only people who do are those who have enough money behind them to give them other options. Or those who are extremely reckless.
MPs should not vote for Article 50 until they are sure what it means | Flip Chart Fairy Tales