I will shortly leave London for Washington after a memorable four-year assignment as Ireland’s ambassador. I will depart with deep affection for this country where so many Irish people have made their homes, and to which they have contributed hugely. The past four years have been a wonderfully positive time for British-Irish ties, and the first state visit by an Irish president in April 2014 was a particular highlight.

On the downside, I have been dismayed to have witnessed the UK’s move to leave the EU and the continuing fall-out from that fateful decision. Indeed, Brexit represents the main cloud on an otherwise sunny horizon for my country, where our economy is growing robustly again.

Having closely observed the debate about Brexit, I still fail to see its rationale. It appears to be based, in part at least, on misapprehensions about the EU’s nature and purpose and on a degree of disdain in some quarters for the Union’s undoubted achievements in facilitating a long era of peace and prosperity in Europe.

I accept, of course, that Brexit is a matter for decision in the UK, but its implications do not stop at Britain’s borders and it poses major challenges for Ireland. There are huge economic interests at stake. The flow of trade across the Irish Sea is significant — more than £1 billion each week — sustaining jobs and prosperity. Both of us therefore have an interest in preserving those benefits, which is why we in Ireland hope that the UK will ultimately decide to remain in the customs union and, ideally, in the single market too. There are real apprehensions about the possibility of barriers being erected after Brexit, not least in Ireland.

Let me be clear: we wish Britain well for the future. We have a vital interest in a Britain that is outward-looking, prosperous and on good terms with its neighbours. We will do what we can to facilitate a positive outcome to the negotiations on future relations between the UK and the EU. We hope that a new partnership can be created that will keep the UK closely aligned to the European Union, but that will require flexible approaches to prevail.

As I depart from the UK, I still hope that a sensible settlement can be arrived at, but this will require a formidable effort to understand and accommodate each other’s concerns. As these complex negotiations evolve, I sincerely hope that our friends in Britain will keep the Irish dimension of Brexit at the front of their minds. That is where it needs to be if both our interests, economic and political, are to be appropriately nurtured for the benefit of this and future generations of our neighbouring, deeply interconnected peoples.

Daniel Mulhall is Ireland’s Ambassador in London.