John Delius is a retired university lecturer.

“For want of a nail … the kingdom was lost”.  This proverb speaks to Brexit.

You can’t win a war without efficient logistics. If one box of spare parts for the Tornadoes or the tanks is mislaid, the whole war may be lost, and a leader who orders the troops to fight a war with a defective logistics system is unlikely to win.

In a modern war logistics are managed by huge computer systems, and the Brexit equivalent of the nail is the computer authorisation for a thousand transport movements (a small fraction of one day’s worth). There is a serious risk of chaos at the docks and airports, because the Brexit changes to the terms of trade with the EU and other countries will require thousands of changes to be incorporated in very complex computer systems.

It’s like this. The whole life of this country, and of the EU generally, depends on smooth and uninterrupted passage of goods in both directions.  The quantity of these goods going in each direction each day is enormous: 6,000 lorries, with thousands of containers, pass through Dover daily.

Customs authorisation for import or export depends on the codes for the goods, the country and place of origin, and whatever conditions may have been made by the EU or Britain and entered on the system. Every type of good imported or exported has a category code; there are tens of thousands of these codes.

Only a very few loads – dangerous goods or suspect trucks – are checked by a human operator.

The whole system runs pretty smoothly. It has to. Supermarkets, that import a lot of our food from the EU and elsewhere, have their food lorries unload at huge depots where the stuff in each container – which may be that supermarket’s national supply of milk for a day or oranges for a week – is divided up, some for each of their outlets around the country.

Every day we import 30 lorry loads of milk from Belgium, Holland, and Ireland and 15 lorry loads of oranges. Now, suppose there is a hold-up at Dover. No milk or oranges in Quikko supermarkets! Panic buying at the others!

Real-time systems cannot deal with uncertainty. The old code may have been cancelled but no new code notified, or contradictory instructions issued, both of which are common products of bureaucracy.  Every lorry must be either accepted or rejected, and if rejected, will have to be dealt with by human intervention, in which case the truck is sent to a parking area.

Even one rejection or ‘don’t know’ per hundred lorries will quickly result in overflowing lorry parks. And if the whole area around Dover becomes blocked with trucks (as happened recently when the Channel Tunnel was closed over illegal immigrants) there will be unpredictable food shortages all over the country.

The detailed Brexit negotiations are highly unlikely to be completed in two years, and even if they were, converting them into computer language and entering them all will take a year or more. While the system can cope with a few changes to the rules every week, trying to change thousands of complex codes and regulations in a short time is sure to introduce errors.

The larger the system and the more changes you make, the more faults and unexpected outcomes you get, the more likely the whole system will crash and the worse the resulting chaos. How to insure against this outcome is the apparently unrecognised problem for the Brexit planners.

A wise leader doesn’t order his generals to fight a war when there is no way of supplying the troops in the battle zone – yet politicians are telling the civil servants to negotiate with 27 countries about importing this and exporting that, when they have no idea how the decisions can be practically implemented. “For want of a nail…”

So how do we prevent this situation of likely chaos? Here’s my suggestion – call it the Carey system:

The basic principle: all British import and export rules and regulations will continue unchanged for the time being, unless and until otherwise decided, notified and entered on the computer systems. We invite each EU country and our other trading partners to do likewise.

Since it is in the interest of every EU country that their exports to and imports from Britain are not suddenly interrupted, when they realise a likely alternative is transport chaos, they will individually agree with us to implement this policy on their side of the Channel too.

With each country we will set up a small bilateral committee, empowered to make an immediate real-time decision on every query needing an immediate answer. These committees will deal with all urgent questions to which the computer system cannot give an answer. They must operate an efficient, real-time method to release lorries that are stuck because the system can’t authorise them to proceed.

Uncertainty in import-export trade is a serious hindrance, and we must reduce it as far as possible. These proposals will remove uncertainty from immediate business decisions, reduce the risk of chaos at the docks, and permit life to carry on as usual while the changes required by Brexit are gradually and smoothly introduced.

There are also some useful side-effects of the Carey system: first, it’s biased in favour of free trade, which is in our interest; we are offering other countries unimpeded flow for their goods, and if they reject the offer they harm their own economy.

Second, while offering friendship to all, we have a simple, immediate, direct means (adjusting the computer codes) of retaliating against any EU country that threatens to act in an unfriendly way towards us.

Third, the pressure of deadlines to complete negotiations hastily and without due consideration is removed, whilst the discussion of practical steps towards an orderly Brexit will reduce general fears and the expectation of continued trade with only gradual changes will increase business confidence on both sides of the Channel.