Despite what some journalists are saying, the reason that Leave does not have a plan is not because they are incompetent or lazy (though some of them may be either, or both, of those things). Unusually, this isn’t cock up, it’s conspiracy.
I’m willing to believe that most people who voted in the referendum knew what they, personally, were voting for. But collectively Leave has always been a coalition of inconsistent goals.
Some people voted for free trade. Some people wanted to protect British industries and more state subsidies. Some wanted smaller government. Some wanted more agricultural subsidies, some wanted them abolished. Some wanted to use the money for the NHS. Some wanted a significant reduction in immigration, others wanted to change where the migrants came from. Some were prepared to sacrifice some jobs and incomes for sovereignty; others put the economy first.
Individually they may each have known what they were voting for; but there is no version of Leave that Leave voters agree about. Even if you could assemble a consensus from these contradictory views, it would not be an available option (for example, you might find there was support for frictionless trade but not for the internationally-agreed rules and standards which make this possible).
The 48% who voted to Remain, plus a substantial group of Leave voters, would prefer to stay in the EU than to accept the “vassal state” version of Brexit that Mrs May now proposes. There is an even bigger majority who prefer Remain to a hard WTO-terms Brexit, as proposed by Jacob Rees Mogg. In a head-to-head between Remain and any specific version of Leave, Remain would win.
Dominic Cummings, one of the organizers of the Leave campaign, has written that they took a conscious decision in 2015 to use the slogan “take back control” rather than set out a specific vision, because they knew that anything more specific would shrink their coalition. The Leave campaign’s best hope is, and always has been, to hold a broad, contradictory coalition together for long enough to get the UK out of the EU, and they can only do this if they avoid specifying what sort of Brexit they want.
That is why they were so desperate to trigger Article 50 immediately, and why they have opposed any sort of parliamentary oversight over Brexit. They know that once we are out, it will be much harder to get back in.
The pro-Brexit media (such as James Forsyth at the Spectator) complain that Brexiteers have bungled the process by failing to set out their vision. David Davis’s resignation letter is being presented as the most recent missed opportunity. But Leavers have no choice: they are holding on to the roller coaster for dear life, hoping nobody can find a way to stop it before Britain leaves.