It's essentially a choice of a harder or softer Brexit. Harder prioritizes border control over trade. UK firms would pay tariffs to do business in the EU, and vice versa. The softest Brexit would see access to the single market, or at least a customs union, maintained. That would require concessions — including the payment of a hefty "divorce bill" — to which the UK has provisionally agreed.

Businesses have expressed concern about a "cliff edge" scenario, where Britain leaves the EU with no deal. Even if an agreement is reached at the EU bloc level, the worry is that it could be rejected at the last minute. Each of the 27 remaining countries must ratify the arrangements, and any might reject them. That could mean chaos for businesses and individuals.

If there is no agreement at all, a fully sovereign UK would be free to strike new trade deals and need not make concessions on the rights of EU citizens living in the UK or pay the financial settlement of outstanding liabilities. However, trade would be crippled. UK citizens in other parts of the EU would be at the mercy of host governments. There would also be a hard EU-UK border in Ireland.

The EU and the UK could reach a deal on Britain's exiting the bloc without an agreement on future relations. This scenario would still be a very hard Brexit, but would at least demonstrate a degree of mutual understanding. Trade agreements would be conducted, on an interim basis, on World Trade Organization rules.

Most trade tariffs on exported goods are lifted, except for "sensitive" food items like eggs and poultry. However, exporters would have to show their products are genuinely "made in Britain" so the UK does not become a "back door" for global goods to enter the EU. Services could be hit more. The City of London would lose access to the passporting system its lucrative financial business relies on.

Under the Swiss model, the UK would have single market access for goods and services while retaining most aspects of national sovereignty. Switzerland, unlike other members of the European Free Trade Area (EFTA), did not join the European Economic Area (EEA) and was not automatically obliged to adopt freedom of movement. Under a bilateral deal, it agreed to do so but is still dragging its feet.

As part of the European Economic Area, Norway has accepted freedom of movement – something that no Brexit-supporting UK government would be likely to do. Norway still has to obey many EU rules and is obliged to make a financial contribution to the bloc while having no voting rights. Some see this as the worst of both worlds.

Turkey is the only major country to have a customs union with the EU, as part of a bilateral agreement. Under such an arrangement, the UK would not be allowed to negotiate trade deals outside the EU, instead having the bloc negotiate on its behalf. Many Brexiteers would be unwilling to accept this. It would, however, help minimize disruption at ports and, crucially, at the Irish border.