Over the weekend Liam Fox, secretary of state for international trade and generally regarded as one of the more fervent Brexiteers in Theresa May’s government, suggested that the UK might remain part of the EU’s customs union even after it gave up full EU membership in two years’ time. Previously, he had seemed eager to make a fast, clean break.

Even if his comments referred only to a temporary transitional arrangement, they imply a significant change in his view of how Britain should leave the EU.

How would remaining in the EU’s customs union work?

Essentially, it would mean that Britain agrees to set common external goods tariffs against non-EU countries. It would enable UK goods to continue to circulate freely within the EU without the fear that other countries were using Britain as a backdoor to export into the EU market.

The closest model is Turkey, which has had a customs union with the EU since 1995, though in Turkey’s case this covers only industrial goods, not agriculture. Customs unions have a long history in continental Europe: the Zollverein was a 19th-century version that brought together disparate states of pre-unification Germany.

What are the advantages?

First, simplicity. This is particularly true if the customs union is a transitional arrangement for a few years while the UK decides what its long-term trading relationships are going to be. It is highly unlikely Britain would be able to negotiate any bilateral trade agreements within the two-year process of leaving the EU, so continued customs union membership would ensure goods could continue to travel freely across borders.

And the benefits in the longer term?

Membership of the customs union would ensure goods were not subject to import tariffs or — probably more importantly — to checks that they met EU standards. Nor would UK exports to the EU have to be subject to “rules of origin”, which prevent Britain being used as a backdoor. Sometimes more is made of these checks than is warranted: Norway, for example, which is not part of the EU customs union, manages to export into the EU through Sweden without having to have every consignment checked, and Britain might do the same at the Northern Ireland border. But there is no doubt that the extra paperwork does impose some costs.

Staying inside the customs union also gives companies more confidence that they can build up supply chains without trading arrangements suddenly changing.

So why not stay?

One of the key arguments for Brexit was that the UK could broaden its horizons to trade with the rest of the world. In effect, Britain would not be able to sign goods agreements with other countries as long as it was obliged to maintain a common external tariff. If agriculture was included, for example, the UK would not be able to give British households cheaper food by cutting farm tariffs.

Moreover, when the EU signs preferential deals with other countries — it has pacts in place covering dozens of trading partners — the UK will either be obliged to follow suit or to lose competitive advantage against those nations. The EU-Turkey customs union is generally regarded as an uncomfortable arrangement by both parties for this reason. Turkey asked to be allowed to participate directly in negotiations between the EU and the US for the Transatlantic Trade and Investment Partnership (TTIP) rather than simply trying to replicate it after the fact, but was rebuffed.

In theory, even from within the customs union the UK could still sign trade deals with other countries covering issues such as product standards and services trade. But British exporters will still have to adhere to EU standards if they want to export to continental Europe, leaving them subject to swathes of European legislation. And countries will be reluctant to sign a services-only agreement allowing in UK companies without getting reciprocal access for their goods exporters. The US, for example, is loath to sign bilateral trade deals without levering open overseas markets for its farmers.