Britain needs to prepare for a failure to meet the two-year Brexit deadline. United Kingdom Prime Minister Theresa May’s unfortunate letter to European Union (EU) President Donald Tusk turned out to be a simplistic exercise in optimism. She blandly offered a very similar exit deal to the one that she has been touting around the country, but included an expectation for a parallel negotiation on the UK’s future relationship with the EU. The EU has already dismissed this as impossible, and insisted that the exit talks must precede the new relationship.

This raises the ugly possibility that at the end of the two-year process, the deadline will not be extended and Britain will have to leave without a proper agreement. London has persistently failed to understand that the implementation of the departure from the EU of any country that has triggered Article 50 must happen after two years, unless the 27 remaining members of the EU all separately agree to an extension, which they may not wish to do.

This means that all sorts of countries could use the opportunity to rake up old quarrels. Spain could refuse to extend unless Britain offers a compromise on Gibraltar; Cyprus might seek more support against the Turkish occupation of its northern half; Latvia might seek a better visa deal. All sorts of things could emerge that might wreck the talks.

The problem with May’s letter was that it failed to offer very much for the European side to work with. She has called for a “bold and ambitious” free-trade agreement including financial services, data and telecoms, which is very similar to the current single market, but she also insists that Britain will have nothing to do with the European courts or the free movement of people that the EU has repeatedly said is vital for a single market. May has offered no movement on how Britain might compromise over this in order to win the trade agreement that she wants.

So a clash is already very likely. Although the letter did not repeat her January threat that “no deal is better than a bad deal”, May said in her letter that it is possible that Britain will leave without an agreement. Tusk hoped for an orderly exit, but he also added that he and the EU negotiators would “protect the interests of the 27 remaining EU members”. This is not a hopeful start to a painful two-year drama.