It is a year since Article 50 was triggered, starting a two-year negotiating period in which the withdrawal process was intended to be completed. In fact, it is only this month that the process has begun. This gives six months to complete it, given the need for ratification by the European and national parliaments.

There is agreement on a 21-month transition or, as the UK Government calls it, implementation period. It is neither, but rather extra time to negotiate the future relationship. During that time, the UK will remain subject to all EU laws without having a vote.

The future relationship is anything but clear. The UK Government, supported by Labour, insists that the UK will be out of the EU Single Market while keeping many of its benefits. The EU says that there will be no such cherry-picking. Conservatives and Labour both want to withdraw from the EU customs union but the Conservatives want a ‘customs partnership’ while Labour would keep a (not the) customs union. Neither has convincingly explained what this means.

Deadlock remains over what happens to powers currently held by Europe over devolved matters. The UK Government has retreated from its plan for a blanket reservation of these powers and has sought legislative consent to the Withdrawal Bill from the devolved legislatures. There is agreement on the principle of common UK frameworks in key areas. Yet, with the Withdrawal Bill in its final stages in the House of Lords, there is no agreement on how to amend it and no legislative consent. Everyone wants to avoid a hard border in Ireland but nobody knows how. Three options are in this month’s agreement. The first is that the issue will be resolved in the overall future relationship between the UK and Europe. That is not possible if the UK is outside the Single Market and customs union.

Second, the matter might be resolved by technology, as the UK Government believes, but that is a way of managing border controls, not eliminating them. The fall-back option is for Northern Ireland to retain regulatory alignment with the EU, which means either a special status for Northern Ireland or the whole of the UK keeping regulatory alignment. Neither is acceptable to the UK Government or its parliamentary allies in the Democratic Unionist Party.

Both sides have used the slogan ‘nothing is decided until everything has been decided’. That is a big challenge in a short time.

Michael Keating is Professor of Politics at the University of Aberdeen and Director of the Centre on Constitutional Change.