Brexit: what now? The government lobbed a hand grenade into the Brexit talks this week, by revealing it was ready to break international law by overriding the withdrawal agreement Boris Johnson approved less than a year ago. Negotiations on a trade and security deal, nevertheless, stagger on as planned. Informal talks continue for the next two weeks, culminating in the ninth round of negotiations from 28 September to 2 October. The end of September is also a moment of reckoning: the EU has threatened to take legal action if the government goes ahead with the current version of the internal market bill. If the UK ignores its obligations, it is hard to see talks continuing. What if the government changes course? If the government backs down on the bill, or is defeated in parliament, a Brexit deal is back on the cards. Talks will intensify. But time will be tight: one of the few things the prime minister and the EU agree on is that any deal must be done in October. Johnson has said there needs to be an agreement by the EU leaders’ summit on 15 October if it is to come into force by the end of the year. The EU chief negotiator, Michel Barnier, has set a deadline of the end of October. His officials have deliberately pencilled in an extra two weeks, expecting a final sprint to the finish after the summit. Why October? The Brexit transition period ends on 31 December, but both sides, especially the EU, have a lot of work to do to get the treaty ready on time. If and when Barnier strikes a deal with his UK counterpart, David Frost, the EU will have to accelerate legal processes and political decisions that take far longer in a conventional negotiation. British and EU lawyers will go through the text with a fine-tooth comb to check for errors, a process known as “legal scrubbing”. The document will have to be translated into most or all of the EU’s 24 official languages. Meanwhile, some EU27 governments must consult their national parliaments – even if no ratification is required by national and regional assemblies – to guarantee political backing at home. “Several countries cannot give a green light unless they have had an OK from their own parliaments. This is not something that can happen in a super-Saturday-style way,” said one EU official. Don’t EU talks always go into extra time? Very often, yes. And some Brexit watchers think the deadline could stretch to mid-November. EU officials, however, insist the end of October is a hard deadline, citing the volume of work required to turn the deal into a legal treaty, expected to run to 1,000 pages. “The end of October is a genuinely hard deadline,” said the EU official. “I honestly physically don’t know how things would work in a shorter time. Normally we would do this in 18 months. But I know no one in the UK believes that.” David McAllister, a German Christian Democrat MEP and close ally of the chancellor, Angela Merkel, told the Guardian “a ready text must be available by the end of October” to start ratifying the agreement. “This is not a technocratic position, but a legal requirement. The council [of EU ministers] and the European parliament must have the necessary time to scrutinise the agreement and give their consent. We have expressly communicated this to the British side.” What happens on 31 December? Brexit. By automatic operation of the law, the transition period ends and the UK leaves the EU single market and customs union. Even if there is a deal, changes for businesses trading with the EU will be immense. Companies face new paperwork to import or export goods from the bloc, with yet more processes required for certain goods, such as chemicals, alcohol and tobacco. The Kent lorry park will open its gates as the extra paperwork kicks in. Experts have warned that the “just-in-time” production system on which the British car industry relies is unlikely to survive the onslaught of red tape. Travellers will face restrictions: mandatory checks at the EU border (excluding the Anglo-Irish common travel area) and limits on how long they can stay in the bloc without a visa. Tourists will have to get by without pet passports, the European health insurance card and the right to drive on the continent on a UK licence. In the event of no deal, farmers and manufacturers will be hit with tariffs. With the EU supplying nearly one-third of the UK’s food, it’s almost inevitable that some items will become scarcer and more expensive. Lorries will be delayed at the border, possibly for a few days. Hundreds of EU fishing boats could be operating in British waters illegally, sparking skirmishes and blockades at ports. And Britain’s relationship with the rest of Europe will hit a nadir that will take a long time to repair.