They didn't know what the EU did and didn't know how they did it. So, it's no surprise they didn't know how to organise leaving.

then I read this. In it he talks about the dangers of people in Government who simply hve no idea of what their departments do or how they do them.

Guardian - Alex Bladsel - Michael Lewis: The Big Short author on how Trump is gambling with nuclear disaster

Lewis was contemplating the nation's dire risk portfolio when Trump tapped the former Texas governor Rick Perry to be secretary of the Department of Energy. Five years earlier, Perry had said in a presidential debate that he wanted to eliminate that cabinet-level department. At least, he had tried to say it: in a moment that helped sweep his ruinous candidacy into oblivion, Perry forgot the department's name.

"It's bad enough Rick Perry has no sense of this," Lewis thought after hearing of his appointment. But he had to acknowledge he didn't know anything about the department either. So he decided to find out. "It took about two phone calls before I learned, `Oh, that's where the nuclear weapons are. Oh my God.'"

What Lewis went on to discover was even more shocking. On the morning after the presidential election, as the balloons from the previous night's parties are still settling on the ballroom floors, the president-elect is expected to send teams into every department of the US federal government to begin the transition of power. But at the Department of Energy last November - and, it turned out, at many of the country's 14 other federal departments - one day passed, and then another, and no one came.

Bureaucrats in the Obama administration had worked for a year to prepare thousands of pages of briefings on the risks their successors could face. Yet by Thanksgiving, no one from the Trump team had arrived to receive them. "I was fucking nervous ... ," Steve Bannon later told friends about Trump's handling of the transition, Lewis reports in the book. "I go, `Holy fuck, this guy doesn't know anything. And he doesn't give a shit.'"