The British used to rule 1/4 of the world's landmass and 1/3 of the world's population. To say this gave them a god complex is an understatement. I mean, shiat, the monarch's motto is "God and My Right", as-in, even if God His Own Damned Self told the monarch to fark right off, the monarch still trumps God by their very existence because they have more right to rule than just a mere Yahweh. And the rest of the British think the monarch is a wanker. So, they are more entitled than the guy/gal who thinks they are more entitled than God.
Now, after WWII, Britain's empire was what is called in technical jargon "farking gone", while their economy was essentially negative - they still had rationing nine years after the war ended. So, they needed to enter into an economic relationship with the rest of Europe if they wanted to eat and run off to terrorize Spanish children as a vacation. This then grew into the political relationship called the EU. But, despite gaining entire swaths of economic advantages from being in the EU, as well as a ridiculous number of exemptions from various EU rules, remember that the British think that God is their biatch's biatch, so having to do things like share, and be nice to, and not rape others was seen as a terrible imposition upon them.
So, that out of the way, in 2010 the Tories (the Conservative Party) almost won a Parliamentary election. They got the most seats, but not a majority of the seats. But, if they could make nice with another party that had enough seats to get a majority, they could run things. Along came the Liberal Democrats. Usually, if you are being asked to help out, you ask for as much as possible to join, negotiate down to something reasonable, and then hang around until you can throw a monkey wrench in things. The Lib-Dems asked for essentially nothing, and basically agreed to have the Tories punch them in the face whenever something went wrong, even if the Lib-Dems had nothing to do with the problem the Tories caused. There are women in East Alabama trailer parks that have more self-respect than the Lib-Dems had.
But, hey, the biatch might leave you and take the Franklin Mint Collector's Plates. So, David Cameron, head of the Tories, wanted a real majority in the next election of 2015. One problem though. There really was no serious room for the Tories to move centerward if they wanted to maintain their core values of hard-right dumbfarkery. So, they looked farther to the right.
Enter UKIP. UKIP is the British Nazi Party, except they think the actual Nazis were way to nice to the Jews. And UKIP hates the EU, because it has too many, ie any, non-British living there. So, UKIP's only issue is leaving the EU.
So, Cameron ran the 2015 election promising a referendum on leaving the EU. He was going to give UKIP voters what they wanted. Now, UKIP has had a grand total of 1 MP. You need 326 to have a majority. Those numbers are not very close. And you need to be in the majority to propose such a referendum. So, UKIP voters could vote uselessly for UKIP - or vote Tory and get their fondest wish. They voted for the Tories and Cameron got his majority.
Something to be clear about. Cameron did not want to leave the EU. Most Tories didn't want to leave the EU. No matter how much they hated it for existing while not being a British colony, they also liked the money it made them. So, Cameron felt duty-bound to carry out the referendum he promised, but he was adamantly against it. He wanted it to fail. He expected it to fail.
As did everyone else. The "non-binding" part was put in by Nigel Farage, head of UKIP. His schtick has always to be elected to the European parliament (since no one in Britain cares enough to vote for those, and so his little cadre of cultists could carry the day). He then biatches about being in the EU - you know, the people paying his salary. But if a "binding" resolution failed, he couldn't biatch anymore. And he expected to lose. Big time. They were expecting Brexit to garner mid-teens.
So, Brexit was a campaign stunt meant to garner the Tories a parliamentary majority. That was it's purpose. And it did that. And it was supposed to die after that. Die and be forgotten.
Thing about everyone - including the proponents - thinking the whole thing will be a massive failure. It makes the need to give a flying fark non-existent. You aren't going to propose serious plans, because why waste effort for something that will not, cannot, happen? If I told you that if you won 4000 consecutive roulette spins (picking one number), that you got to fark [insert the fark-honey of your dreams], would you actually go out and buy some condoms? So, the pro-Brexit people just made up shiat. They wanted the numbers to not look pathetic, so they hoped to gin up a little support around the edges. And they made different promises to different demographics, almost all of said promises being mutually-incompatible. After all, if you never have to deliver, then who cares? Except, many people had low-level complaints about the EU. Nothing serious, just usual "why government not jack me off?" stuff. And along come these guys promising handjobs and cocaine to everyone. And all those little bits and bobs turned into a bare majority.
The Russians also looked at this kerfuffle and decided to stir the shiat because Putin has very little actual international power and asymmetrical warfare is all about stirring the shiat. But the reasons for the vote and the reasons it developed as it did were purely British inside baseball politicking. The Russians definitely goosed the numbers up, but Putin did not create Brexit as Athena springing from the head of Zeus. It was more he saw two drunk idiots about to start a fight anyway, egged them on, and stole their wallets in the donnybrook.
Cameron retired when Brexit passed. He had brought it up, but he was its biggest opponent, even threatening voters if they voted for it. Imagine Obama threatening to send the Marines in to "sanitize" any district of a Congressman who voted for Obamacare. So, when it passed, he jumped ship.
At the same time, the Tories were frankly flat-footed. Where did all these Euro-sceptics come from? Were they there all the time? If the Tories won an election by sucking off a few Euro-sceptic cranks, what could they get if they deep-throated all these people eager to leave the EU? So, practically overnight, the Tories became more anti-EU than UKIP ever dreamed of being.
They had no plan. Didn't need one for the referendum that would fail. All they had was a bunch of contradictory promises made because they would never have to be kept. But which ones were needed to keep all these Brexit voters, and which could be tossed aside? No idea. Because the Brexit majority were a whole lot of small niche groups Frankensteined together with spit and baling wire. Well, to leave the EU, they needed a plan. So, they Tories went to their playbook and came back with ... slag the EU like Klansmen throwing down at the NAACP for two years. Demean everything, give nothing, shiat in the punchbowl, declare victory. While the EU was sitting there trying to discuss substantive issues of separation. So, you get one party in a divorce trying to come up with a way to divide assets, while the other is Andy Kaufman on PCP. And the UK never changed its routine the entire time.
Finally, the UK was so determined to leave the EU that they all agreed the UK would leave in January 2020, but they would use the rest of 2020 to work out the plan that was supposed to be done two years prior. The Tories spent 2020 slagging the EU and refusing to do a damned thing.
So, 2021 is here, and there is no actual plan, and the UK is mortally affronted that the EU won't let them sleep in the house anymore, give them handjobs, and share the bank account anymore. And in true British fashion, this is not their fault, but the evil EU for being all European and shiat.
Meanwhile, Trump wanted to economically rape the UK blind for Supply Side Jesus. And Biden is looking at the respective economic resources of the EU and UK, and can't get away from the fact that the EU offers more and better deals, because soggy mashed potato pasties are not going to sell in the US for $7000 a pop just to keep the UK economy slightly better than Malawi's. So, the UK is right and proper buttfarked, with no plan to stop the right and proper buttfark, and no understanding that they have dropped their own trousers and are desperately shoving a doorknob up their own asshole while everyone else at the christening are just trying to ignore the guy forcing himself to be anally penetrated by the rectory door hardware.