Brussels - The European Commission warned Britain Tuesday it should make an "orderly" agreement on the terms of its divorce from the EU including its exit bill before any talks on a future trade deal can begin."If one wants to divorce but remain friends on the basis of a new relationship, first one needs to agree on the terms of an orderly separation," commission spokesperson Margaritis Schinas told reporters."An orderly separation where both sides honour the obligations, and then on the basis of this build a future new, good relationship."Under the two-year exit period set out in EU treaties, a country leaving the bloc must finalise a withdrawal agreement on issues including outstanding membership costs and citizens' rights, EU officials say.But until now Brussels had declined to say if talks on a new trade pact can take place in parallel with those on the withdrawal deal, or if the withdrawal agreement must be completed first, a process that could take months.The withdrawal agreement includes the bill Britain must pay to leave, an EU source told AFP.The EU has estimated Britain's departure bill at €55bn to €60bn, which covers budgetary requirements and pension liabilities, European sources said.Separately European Commission Vice-President Frans Timmermans warned Britain that it could not make new trade deals with other countries like the United States until it has left the EU.US President Donald Trump has promised to push through a deal with Britain, and is meeting Prime Minster Theresa May in Washington on Friday."It's a very simple legal situation, everybody can talk to everyone but you can only sign a trade agreement with someone once you've left the European Union, you can't do that before," he said at talks in Malta.The warnings by the executive arm of the 28-nation European Union came as Britain's Supreme Court ruled that May must get parliament's approval before triggering Brexit, which she has promised to do in March.The European Commission's Brexit negotiator Michel Barnier has said that Britain and the EU will need to wrap up all talks by October 2018 to give the EU and national parliaments time to approve a deal within the two-year window.