No case can be made for bumbling along in the hope that a deal will turn up.
It is a sign of how fevered our reporting has become that it is considered odd for the foreign secretary to write a memo to the prime minister about foreign policy. What is odder still is that demanding proper preparations for a no-deal departure from the EU should be regarded as remotely controversial.
No one wants a breakdown in the talks: we have an interest in the welfare of our neighbours, and should seek as amicable a settlement as possible. Equally, no one should go into any negotiation without a bottom line.
Failure to prepare adequately for unilateral withdrawal will, paradoxically, make it more likely, because it will encourage those in Brussels who believe that, if they offer harsh enough terms, Britain will somehow drop the whole idea of Brexit.
If you are reading this article in the UK, you know that that won't happen. None of the big parties is challenging the referendum outcome, public opinion has not shifted since the vote and, in any case, Brexit is a legal reality: we leave on 29 March 2019 with or without an agreement.
When even Michel Barnier is preparing for a no-deal Brexit, it would be criminally negligent not to have adequate preparations in place on this side of the Channel.
As I have argued here before, putting adequate preparations in place doesn't mean circulating contingency papers among civil servants; it means making the actual changes so that, for example, our driving licences, patenting rules and airline slots work independently within the global system.
Ministers occasionally say that the necessary work is being done, but I'm not sure they are believed in Brussels. Hence Michel Barnier's slightly curious remark that, without a deal, British planes won't land in Europe and the pet passporting scheme won't apply.
We have aviation agreements with every country in the world, and the EU's rules on pets extend to every major country from the US to Japan, as well as quite a few minor ones. Is Michel Barnier seriously threatening us with a blockade? If so, all the more reason to get ready now.
As far as I can see, the UK has three realistic options. One is to join the European Free Trade Association. The second is to postpone our departure date to 31 December 2020, solving almost all of the outstanding financial issues and giving ourselves time to put in place whatever arrangements we need on aviation and the like. The third is to walk away from the talks now, assume no deal, and begin to slash taxes and regulations.
There are arguments to be made for all of these options We can choose to replicate many EU arrangements à la Suisse, seeking to remain in a European market and to minimise the disruption.
Or we can choose to be a buccaneering, high seas nation, which makes full use of the recovery of its domestic regulation and trade policy to become a North Sea Singapore.
There is also a case for something in between the two – starting, so to speak, with a Swiss-style arrangement and gradually diverging over time.
A case, as I say, can be made for each of these options. But no case whatever can be made for failing to pick any of them, and bumbling along in the hope that something will turn up.
Businesses can be reassured in one of two ways. Either they can be told that the regime under which they are currently operating will be maintained with only a few tweaks (the EFTA option); or they can be told that Brexit will be followed by a radical reduction of tariffs, corporate taxes and regulations. It's time to choose.