Laurent Bonnaud is an economic historian and founder of Sponte sua sprl, a public history consultancy based in Brussels. He has written extensively on transport networks.

For centuries, the French military defended the country’s coastline whereas the Royal Navy prevailed over the English Channel. Promoters of a submarine tunnel drafted a definition of the border in the 1870s. But the tunnel was not completed and the status quo was maintained.

In 1973, another Chunnel project and the UK accession to the EC reopened the issue. Britain renounced to the tunnel in 1975 and it took another decade to sign the London agreement of 24 June 1982 on the continental shelf.

Negotiations for a Fixed Channel Link succeeded in the mid-1980s. The UK favoured immigration controls at ports and airports and in France throughout its territory. Meanwhile, the EC made the abolition of border controls a priority for 1992.

The Fixed Link would carry millions of passengers and tons of freight through twinned undersea railway tunnels. Achieving these goals while maintaining the highest possible degree of safety and security was a daunting challenge.

On 12 February 1986, the Treaty of Canterbury defined the first physical border between the UK and the continent as the vertical projection in the tunnels of the line agreed in London in 1982. An Intergovernmental Commission was to supervise the Fixed Link.

Juxtaposed controls on leaving the territory, as in transalpine tunnels, were finally agreed upon and options retained for controls on entering the territory and on board trains.

The Sangatte Protocol of 25 November 1991 opened a long series of bilateral arrangements and political declarations. They met the specific needs of the Fixed Link on border controls, police and judicial cooperation in criminal matters, civil security and mutual assistance.

On 1 January 1993, free movement of goods and people became a reality within the Single Market of the EU. But ensuring security and safety in the tunnel inaugurated in 1994, including deterring terrorists, was a top priority.

Juxtaposed controls were put in place at terminal installations for the Shuttle, moving the British border to Coquelles, and to Brussels-Midi and Waterloo stations for train passengers. On board checks were carried out on the Paris-London rail service.

In 1995, France joined the Schengen area. The UK and Ireland did not. Controls later extended to Paris-Gare du Nord and Lille stations. On board rail checks gradually phased out.

The short crossing has long made the Strait of Dover an attractive route for illicit dealings. From the late 1990s onwards, numbers of migrants originating from the Balkans and the Middle-East tried to board through-trains or trucks at the risk of their lives. Traffic in the tunnel was disrupted, aggravating the concessionaire’s financial difficulties.

Not without dissension, the French and British authorities have reacted over the last two decades by regularly reinforcing the joint management of the Franco-British border and the protection of the French tunnel terminal and the port of Calais.

The treaties of Le Touquet (4 February 2003) and Sandhurst (18 January 2018) are the cornerstones of this policy.

In the summer of 2020, migrants try to cross the Channel on dinghies. The most recent Franco-British decisions aim at making the sea route unviable.

A genuine overhaul of the legal and institutional framework of the Franco-British border has therefore been put in place since 1986. It extends beyond the letter and spirit of the Treaty of Canterbury. Brexit reformulates this complex equation.

The other Brexit border?

According to the Withdrawal Agreement of 17 October 2019, bilateral arrangements should facilitate cross-border rail services post-Brexit. But the draft Internal Market Bill giving the UK the power to modify the Withdrawal Agreement created huge uncertainty.

Under WTO rules, administrative and customs controls would degrade supply chains highly integrated since 1994. Sanitary and veterinary controls are the most complex to implement.

Efficiently managing the Chunnel and its border will further require a unified set of rules. On 8 October 2020, the European Parliament approved a Commission proposal to keep a single safety authority for the British and French sections of the Fixed Link and to empower France to negotiate with the UK to that end.

The Court of Justice of the EU would remain the arbitration authority. The UK Department of Transport has expressed its view that these proposals are not consistent with the Government’s sovereignty objectives.

In 2019, the Fixed Link carried 1.6 millions lorries, 2.6 millions cars and 21 millions passengers between the UK and the continent. The price of COVID-19 is heavy here too. As of 30 September 2020, lorry traffic was down 13% year-to-date and car traffic nearly halved.

Despite this, the strategic significance of the busiest railway system in the world for British and Irish trade and food supply, express delivery and tourism are strong incentives to defend the spirit of the Treaty of Canterbury.

To cushion the transition, stakeholders put in place technologies known as ‘smart borders’ to automate controls, recruited additional staff and developed new customs facilities and parks, such as the 10 inland border sites announced in the UK on 8 October 2020.

Observers nevertheless predict potential disruptions in 2021 at the very least. This will certainly be the case for incoming lorry traffic. But the Railway Link has considerable capacity available and could accommodate many more direct freight trains, as its promoters predicted in the 1980s. Bottlenecks in the Kent and Hauts de France regions could then be relieved.