As the United Kingdom drifts towards a hard Brexit, the media are strangely quiet about the significance of the Common Travel Area (CTA) between the UK and the Republic of Ireland. Under this longstanding arrangement, which ought to continue even if the UK leaves the EU without a deal, all British citizens who were born in the UK have the right to live, work, receive health care, access education and vote in Ireland, and Irish citizens enjoy the reciprocal rights in the UK.

One of the main political drivers of the Leave campaign three years ago was the idea that the UK would be able to control immigration from EU countries after Brexit. No one mentioned the exception of Ireland, perhaps because they were selling an ideal rather than grappling with the detail.

I first travelled to the Republic in 1969, without a passport or any sort of identity document. I was one of the hundreds of thousands of people each year who have been freely crossing back and forth since Irish independence in 1922. The newly formed Irish Free State agreed with the residual British government not to impose border checks: instead, they would co-operate, enforcing one another’s decisions on immigration status.

The arrangement was suspended during the Second World War, but cross-border co-operation was preserved with a series of fudges. The Republic remained neutral, but thousands of Irishmen sailed in the British merchant navy, and thousands more enlisted to fight in British uniform. The ‘Donegal Corridor’ allowed Allied aircraft to overfly a corner of the Republic, and Allied aircrew who crashed in the Republic were allowed to cross the border and return to active service. Bodies of dead Allied airmen were returned with full military honours.

Since 1945, the British and Irish governments have tried to harmonise their legislation without letting it seem that they are submitting to the wishes of a foreign power. Meanwhile, their citizens have acted as if the border wasn’t there, crossing and recrossing the Irish Sea to work, play and live. The problems might have been reduced when both countries joined the EEC on 1 January 1973, had it not been for the security pressures of the Troubles.

At the height of militarisation in the 1980s I sat amazed in a Ford Fiesta at a border checkpoint in the ‘Bandit Country’ of South Armagh, while my Irish friend insisted to an armed soldier that we would not produce identification because we did not need to. Eventually we were waved through the chicane of blast walls. ‘It’s all symbolic anyway,’ my friend said, ‘they will have checked the number plate from the control tower miles back, and photographed the occupants. They know damn well who I am and who is with me.’

The 1998 Good Friday Agreement reinforced the rights of Irish people to live in either polity. Since then our politicians have muddled on, protecting the principle of the CTA, aware that any alternative arrangement would produce a social and political disaster to dwarf the Windrush scandal. In 2011, the two governments signed a ‘Joint Agreement … regarding co-operation on measures to secure the external Common Travel Area border’.

After the 2016 referendum, I worried that the freedoms of the CTA might be lost, and prepared myself to follow Gina Miller to the High Court to defend the rights I had before 1973. Bipartite negotiations about reciprocal citizens’ rights seemed to be dragging behind the constant arguments about tariffs and the movements of goods. It took the murder of Lyra McKee to jolt the governments into action. The British-Irish Intergovernmental Conference (set up by the Good Friday Agreement) met on 8 May and signed a Memorandum of Understanding to confirm that the reciprocal rights of the CTA would be continued.

‘Whatever the terms of the UK’s exit from the EU,’ Theresa May’s deputy, David Lidington, said, ‘there will be no change to the rights of British and Irish citizens.’ As he was speaking, I was travelling to and from the Republic with only my UK driving licence for identification.

Critics worry that the Memorandum of Understanding has no status in law, but for nearly ninety years the CTA has relied on goodwill and common sense as much as law. As things stand, I estimate that 55 million British citizens have the right to live, work and vote in the Republic of Ireland, and four million Irish citizens have reciprocal rights in the UK. And if anyone tries to change that, I still have the option of the High Court.