Britain had seven free ports at one time, and closed the last five in 2012, focusing instead on “enterprise zones” where clusters of companies are offered tax relief and accelerated planning permissions. The results have been mixed. The new proposals for “supercharged” free ports seek to revive their customs benefits and add on other inducements, which were not permitted under EU rules.

That all sounds fine, but Sunak’s analysis overstates the relevance of the US experience, while glossing over the limits of non-tariff barriers that would remain in the new hubs. To arrive at his figure of 86,000 new jobs, Sunak used the total number of jobs across the US FTZs (420,000) and scaled it to the UK labour force. That assumes these were all new US jobs rather than ones that were shifted from elsewhere, which isn’t the case.

Nor would UK importers and manufacturers benefit from tariff inversions to the same extent. In British carmaking, for example, tariffs aren’t inverted, meaning there would be no savings. Importers of automotive parts from outside the EU’s single market only face tariffs of about 4.5%, whereas they’d pay 10% on exporting finished cars.

According to calculations by Ilona Serwicka and Peter Holmes at the University of Sussex’s UK Trade Policy Observatory, the savings that importers overall could realise in UK free ports would only be a tiny portion of the value of the goods.

The researchers looked at the five UK goods categories in which the inversion is greatest — that is, the difference in the saving from the levy paid on the imported component and what’s paid on the final exported product. They found that, while there’s scope for some savings, the impact on the economy would be minimal. Together, the five categories comprise 1.14% of UK imports.

“The UK has never had a clear strategy and a clear idea what it wants to do with free ports,” says trade consultant Anna Jerzewska. To create pockets of Silicon Valley-type innovation requires a complex web of policies, not a declaration and some border infrastructure.

Free ports, she notes, also don’t eliminate many non-tariff trade barriers. Their exports still face checks and tariffs. Rules of origin principles need satisfying and are made more difficult in a free port. “A free port won’t be viewed as within the customs territory of the UK,” she says, which means it would fall foul of the principle of territoriality. It’s easy to see how these could complicate the UK’s multiple trade negotiations.

Is it worth it?

Is the cost of setting up these zones even worth it, when average customs duties (assuming there’s no EU trade deal in place) are only about 3%? Much of Sunak’s upside depends on how far the government can sweeten the zones through tax breaks and other inducements. Leaving the EU certainly provides more scope for doing that, but World Trade Organization (WTO) rules let countries retaliate against subsidised exports.

Some job creation around the free ports can be expected, but what kind of jobs and will they simply be displaced from elsewhere? The US experience suggests that there are modest employment and wage benefits eventually, but most free port jobs tend to be manual labour.

There are also worries about whether investing in this would come at the expense of British education and training in general. If lighter regulation and tax breaks are what spurs regeneration and innovation, why limit this to 10 places?

It’s no coincidence that the European Commission has introduced new rules governing free ports, citing concerns over money laundering, tax avoidance and other illegal activity. Such fears are based on past experience, but it’s easy to exaggerate the risks now that the UK wants to use free ports to help it compete after Brexit.

For all its limitations, the idea of modern free ports dotted around neglected parts of the country has political appeal. It sends a strong message to voters in the newly Conservative-voting regions in the north that Johnson will put money into port communities and support manufacturing.

But that virtue signalling will come at a price. These hubs only make financial sense with total regulatory freedom and no zero-tariff deal with the EU. Either Johnson wants to use free ports as a threat in the EU trade talks or he has decided already that free ports offer better value politically; in which case, it becomes more likely that Britain either gets no trade deal this year or just a bare-bones one.

Sunak’s think-tank plan for Britain’s free ports may be the tail that wags the Brexit trade dog.

• Raphael writes editorials on European politics and economics for Bloomberg Opinion.

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