Here are the three most important words in political communication: repetition, repetition, repetition. Most people don’t notice most of what goes on in politics. Squalls at Westminster pass most people by, and rightly so: a country that has to fixate on its own politics is a country in trouble. The best political communicators know that by saying the same thing over and over and over again, they can do two important things.

First, they can eventually get their message through to the wider electorate. Second, they can choose the territory on which their opponents must fight them.

Boris Johnson is an effective political communicator. Despite his studied image of disarray, he can and does stick to his chosen script.

Time and time again, Johnson has repeated that he will “get Brexit done by October 31”. He’s even got a countdown clock in No 10, a gimmicky but effective way to underline his message yet again. That message has become the baseline for political debate about Brexit: advocates and opponents are all talking about how and if he might “get Brexit done” by the end of October.

The alleged importance of that date may yet become the central feature of a general election in the next three months. Dominic Cummings, Johnson’s top adviser, is practically daring MPs to block Britain’s exit on Halloween, and give him an excuse for a People vs Parliament election where the Conservatives (and their Brexit Party allies?) ask voters for a clear mandate to finish the job started by the 2016 referendum and finally “get Brexit done”.

Johnson’s message falls on fertile ground. The idea of getting Brexit done, over and finished so we can “move on” and focus on other, more important issues is attractive to many people, and not just ardent Brexiteers. Around Westminster it’s still common to hear politicians and others talking about projects and priorities “after Brexit”, looking forward to the day when political attention isn’t consumed by EU relations.

But here’s a simple, grim fact about Brexit that has been successfully obscured by Johnson’s repetitive focus on the Halloween deadline. Brexit will not be “done” by October 31, 2019. Or 2020. Or 2030. In truth, Brexit will never be “done”.

This is one of the many awful ironies of Brexit. The people selling and voting for it shared some desire to reduce the role of “Europe” in our national life. In fact, leaving will only increase the time and energy we spend considering and constructing our relationships with the European Union.

Leaving means starting a whole new era of wrangling with the EU. For a glimpse of it, look to Switzerland

Leaving is not the end. It’s the beginning. It means starting a whole new era of wrangling with the EU about how our laws, rules, policies, systems and organisations interact. The 27 remaining EU nations will remain our closest neighbours, our major trading partners, our security allies and matter to us in a thousand other ways. Ripping up institutional relationships developed over 40 years will be quick and easy compared to the never-ending complexity of devising and agreeing new ones.

For a glimpse of what awaits us outside, look to Switzerland, which signed its first trade deal with the EU in 1972. It has since agreed more than 100 other “bilateral agreements” — and is still negotiating with Brussels, with no end in sight. Being a neighbour and partner of the complex, evolving EU means permanently discussing your relationship with it.

Here’s another fact: leaving the EU without a deal won’t mean the UK avoids that vast task of agreeing a future relationship with the Union. It will just mean that when the UK comes back to the table to talk about that new relationship, negotiations with the EU are longer, harder and less likely to give Britain what it wants.

It is true, as Johnson says, that a deal serves EU interests more than no deal; both sides pay a price for interrupting trade. But it is also true that that cost falls more heavily on us than them; Britain’s need to return to talks would be greater than the EU’s, meaning we’d start those talks as the weaker player.

The process would be harder too. Leave without a deal and we wave goodbye to Article 50 of the Treaty on European Union, written to enable a member state to leave with an agreement. Britain then becomes a “third country” and talks about UK-EU relations are covered by Article 218. It says that when the EU strikes a trade deal with a foreign country, final approval rests with European governments and parliaments. If we leave without a deal, any subsequent trade agreement we might strikes with the EU would be subject to veto by politicians from Stockholm to Sofia.

Article 218 is just one reason the EU takes a long, long time to conclude trade deals. Talks on the EU’s Canadian trade deal, so admired by many Brexiteers, started in 2009 and ended in 2014. Final agreement came in 2016 but not all the deal’s provisions are yet in force.

So when you see pictures of that countdown clock in No 10, or hear ministers talking about getting Brexit “done” soon, remember this: the act of leaving the EU, something that has poisoned our politics and paralysed our government for three years, is actually just the short, easy start of the endless Brexit story. It’s what comes next that should be worrying our leaders — which is precisely why they’d rather not talk about it.