Remember Brexit? The UK’s vote to leave the European Union took place 175 days ago, but as the end of the year approaches, nobody seems clear on when it will actually happen. On Thursday it was revealed that the UK ambassador to the EU has told the British government that a deal for the withdrawal could take a decade — and still fail.

Sir Ivan Rogers privately told government ministers that a quick and easy decoupling from the EU is unlikely, and that the consensus among other member countries is that Brexit won’t happen “until the early to mid-2020s.”

Attending a meeting of EU leaders in Brussels on Thursday, Prime Minister Theresa May avoided answering a question about the 10-year delay, focusing instead on the issue of immigration, which leaders are due to speak about.

This report will be a blow to May, who is seeking a “smooth and orderly” Brexit — as well as a “red, white, and blue Brexit.” May had hoped to trigger Article 50 by March 2017, but there’s a long list of hurdles to overcome before the UK can leave the EU:

The Courts – May’s plan to trigger Article 50 in March will be scrapped if the Supreme Court upholds a High Court ruling stating the government must get the approval of both houses of Parliament to begin the exit process. A ruling is expected in January. Even if the government wins, the “Remain” side could appeal to the European Court of Justice, delaying things further.

MPs – If the 11 Supreme Court judges side against the government, May and her cabinet could have their plans for a quick Brexit scuppered by their fellow MPs. While they are unlikely to want to stop Brexit entirely — given it was voted for by a majority of UK citizens — they could hold it up indefinitely until they get more details on how the government plans to negotiate its exit.

Article 50 – Article 50 of the Treaty of Lisbon sets out the rules for how an EU member leaves the union. It has never been tested before, but the rules say that once it is triggered, a two-year countdown begins. Triggering it in March 2017 would mean a UK exit by April 2019 at the latest, but given the ambassador’s comments this week, that may not be feasible.

All the other European countries – Even if the UK does get all its ducks in a row and agrees to a free trade agreement with the EU, that deal will have to be ratified by all the national parliaments of the 27 other EU member states, which could prove problematic given the concerns Rogers has expressed.

Scotland – Every council in Scotland voted to Remain in June’s referendum, so it’s not surprising that Scotland’s First Minister Nicola Sturgeon repeatedly says she has a mandate to oppose Brexit and that the consent of Holyrood and other devolved assemblies should be sought before triggering Article 50. There are also serious questions to be answered over how the border between the Republic of Ireland and Northern Ireland will operate post-Brexit.