Following the UK government's notice of withdrawal from the EU under Article 50 of the Treaty on European Union, the UK will cease to be an EU Member State on 29 March 2019 (or earlier, if a withdrawal agreement were to be concluded sooner).

If, by such withdrawal date, the UK has not concluded a new trade or relationship agreement with the EU, or has not agreed a transitional extension of its existing access to the EU single market, there will be a "cliff edge"; this will mean an abrupt end to the UK's participation in the single market and to any favourable terms of access by the UK or the continuing EU Member States to each other's markets. At the same time, the UK will cease to benefit from all of the existing bilateral free trade agreements between the EU and third countries. The so called "fall-back" position will be the WTO arrangements.

This note reviews the impact of a hard Brexit on the UK's trading relationships with EU Member States and also third countries.

The WTO is a multi-lateral and inter-governmental trade agreement. Its key principles and rules are ultimately limited in scope compared with the EU single market. Business and individuals cannot themselves enforce the WTO rules; enforcement is State-led through the WTO's Dispute Settlement Body (with a right to appeal to an Appellate Body).

The obligations on WTO member countries for trade in goods are contained in the General Agreement on tariffs and Trade ("GATT"), and are principally the following: the obligation to grant most favoured nation ("MFN") treatment to all member countries without discrimination, to abide by maximum tariffs as set out in the member country's schedule of commitments; to confer national treatment i.e. equivalent treatment as between national goods and imported goods; and prohibitions (with limited exceptions) on quantitative restrictions on exports and imports. State subsidies of specific enterprises in respect of trade in goods are also controlled, especially export subsidies and import substitution subsidies.

In relation to services, the General Agreement on Trade in Services ("GATS") likewise imposes an unconditional MFN obligation, and also requirements concerning national treatment and market access, subject to the member country having made relevant concessions in its schedule of commitments. Also certain types of market access barriers are prohibited unless they are made the subject of a reservation in the member country's schedule of commitments.

Under the WTO rules, UK exports to the EU would be subject to the EU's schedule of tariffs. The UK and EU could not grant any favourable trading terms to each other for specific sectors without being prepared to grant equivalent terms to other WTO member countries, based on the MFN rules. Whilst the GATT allows member countries to provide more favourable treatment to each other in accordance with a free trade agreement or customs union between those members, this is only the case where the trade agreement or customs union covers substantially all sectors of industry, but it is not permissible in the case of sector-specific free trade agreements.

At present, the UK is a member of the WTO both in its own right and as an EU Member State. It is unprecedented for a member country to make a transition from participating in the WTO through the EU (or any other union) to participating solely in its own capacity. The UK will need to establish its own schedules of commitments under both the GATT and the GATS. It is likely, or at least it has been assumed, that the UK will take over the existing EU schedules of commitments and replicate these in its own national capacity. However, there is some uncertainty as to whether this is a readily available solution. The UK government aims to follow the rectification procedure as opposed to the modification procedure. A rectification covers amendments or rearrangements which do not alter the scope of a concession and other rectifications of a purely formal character, whereas a modification implies a more substantive change. The modification of a schedule requires prior notification with, and possibly payment of compensation to, affected WTO members. The government may need to seek legal clarity on the consequences for the UK it if has not agreed or certified its WTO schedules before Brexit, and possibly make contingency arrangements.

The government will also need to consider how businesses and individuals will be able to petition the government to act on their behalf in enforcing the WTO rules through the WTO Dispute Settlement Agreement, where disputes arise. At present, the EU Trade Barriers Regulation provides a channel for EU businesses to raise such disputes with the European Commission for the Commission to take action before the WTO.

Also, as from Brexit, the UK will no longer be covered by trade defence measures which have been adopted under the WTO rules in favour of the EU, for example countervailing duties and anti-dumping duties. WTO members that are subject to the EU's defence measures might object to the UK taking over the EU's existing measures. The UK will need to establish its own investigating authority to conduct trade remedy investigations and to protect the UK's interests as regards trade defence measures taken against the UK.

Trading under the WTO rules will involve a significant burden on businesses, especially when compared with trading in the EU single market. Import tariffs will obviously increase costs to business even though EU tariffs are relatively low for many manufactured goods. Customs checks will be required on the importation of goods into the EU from the UK and vice versa, and for some purposes, business will have to certify the origin of those goods. Customs clearances may be accelerated in many cases using software tools, but it seems clear that, overall, the requirements will not only impose tariff costs but also increased costs of employing and training the necessary personnel to fulfil these requirements.

The UK's economy is more dependent on services than on goods, and there is much less liberalisation for services under the GATS than for goods under the GATT. In relation to services, tariffs and MFN treatment are not the main issues, but rather internal non-tariff barriers. In practice, WTO member countries are often more liberal in relation to trade in services than is indicated by their schedule of commitments, but absent such commitments there is no certainty or predictability of arrangements on which businesses can rely. For example, regulated business services are not to any significant degree liberalised by the GATS. Moreover the GATS does not liberalise the flow of data across borders, which is seen by industry as a critical aspect of the provision of digital services. Creative industries will need comprehensive intellectual property rights coverage, but the WTO intellectual property arrangements (the TRIPS Agreement) involve a relatively low level of intellectual property protection. Further, a large part of the audio-visual media services generated in the UK are transmitted to the EU, but the EU's schedules of commitments are silent with regard to audio-visual media services, so adoption of the EU's schedules would not facilitate liberalised trade in this area.

Various studies have been produced of the effects on the levels of the UK's trade, of the UK's withdrawal from the EU. A World Bank study of January 2017 predicts a fall-off of UK trade with the EU of -50% for goods and -62% for services if no UK-EU preferential trade agreement is concluded. These negative figures are reduced to only -38% and -48% respectively if such an agreement is put in place.

Such predictions and consideration of the position under the WTO emphasises the importance of the UK concluding a comprehensive new trading agreement with the EU as soon as possible after Brexit and of securing a transitional agreement for continued access to the EU single market in the meantime.