Was your grandmother born in Ireland? Usually a question that people from Great Britain have been asked out of lighthearted interest or because they've be watching Who Do You Think You Are?. But with the approaching EU referendum, genealogy is about to become much more important for many people.That's because if you were born in Great Britain and have an Irish grandparent or parent you can get an Irish passport by applying for Irish Citizenship through Ireland's system of Foreign Birth Registration. Doing so will allow you to claim dual nationality alongside your British citizenship. If the UK heads for the EU's exit door, having an Irish passport could become a lot more valuable as it will allow you to retain your citizenship of the European Union.For some, of course, getting rid of European citizenship is very much the point of Brexit. But the loss of being "European" comes with consequences. The 'Remain' campaign has been keen to highlight the benefits we get from EU membership. Travelling, working, and buying a house in the EU would certainly become more difficult for British people if the UK leaves Europe. But this doesn't really convey how complicated the picture would become on Brexit. Unless (or until) a visa-waiver scheme is negotiated following Brexit many UK citizens will have to adopt a "pay as you go" approach to working or holidaying in EU countries, completing the necessary entry requirements to enable them to travel (as is the case now for travel to non-EU countries). This means that quite a bit of research and paperwork would be needed ahead of each trip. Many of the benefits currently associated with EU citizenship will likely be lost under these arrangements. UK citizens will almost certainly no longer be able to rely on the European Health Insurance Card scheme in lieu of travel insurance. Even if a visa waiver scheme is secured for travel, it will not enable UK citizens to work, study and access support as if they were nationals of the host state. This means that for those who wish to regularly travel to, work in, or study in EU countries, becoming a national of an EU country (and therefore getting EU citizenship) would offer an alternative solution.But changing nationality is often an expensive and complicated decision, to say nothing of the emotional ties of identity that nationality raises. At present 1.2 million people born in the UK are estimated to live in other EU countries. To naturalise in their host country they would have to navigate its immigration and nationality systems and establish their value to its economy before they would be accepted as citizens. If successful, this might mean having dual nationality (for example being French and British) or having to surrender British citizenship altogether (some EU countries, such as the Netherlands, usually require their nationals to renounce other citizenships). This process of naturalisation is almost always difficult. France, for example, requires that an individual seeking to naturalise must have lived in France for 5 years and are able to speak French (a half-forgotten GCSE French probably won't suffice ...).This is why the Irish connection could be so important to many people if the UK votes for Brexit. It gives as many as six million people living in the UK an easier route to getting EU citizenship. Ireland has long maintained generous provisions for UK citizens to take Irish citizenship and both countries permit dual Irish-UK nationality.There are two direct routes to gaining Irish citizenship. The first route, for UK citizens born in England, Scotland and Wales is by having Irish roots in your family tree. If you have at least one Irish grandparent or parent, you can qualify for citizenship. For many years this rule of citizenship has given many footballers born in England the opportunity to play for the Irish national team. Citizenship through an Irish grandparent would only be effective from the date of at which you are registered on Ireland's Register of Foreign Births, so this would have to be completed before you have children if they are to also enjoy Irish citizenship. The second group of people who can easily secure Irish citizenship are those born in Northern Ireland. This arrangement is part of the long history and close connections between Northern Ireland and the Republic of Ireland. A child born to British or Irish parents in Northern Ireland is automatically entitled to Irish citizenship and can therefore apply for an Irish passport without having to complete a citizenship or naturalization process. In short, some people in the UK have more to lose from Brexit than others. Northern Ireland's residents have plenty of other things to be concerned about, but most would be able to retain their EU citizenship if they wanted to do so by applying for an Irish passport.In Great Britain, by contrast, the nationality of your parents and grandparents really could matter if you wanted to continue to enjoy full access EU countries. For Ireland, these arrangements could pose problems. If they become too popular as a backdoor to the EU, it might have to reconsider its generous citizenship rules. Waiting times for processing Irish passport applications are already lengthening and a constant stream of people living in the UK and making use of the 'granny rule' might lead to pressure from Brussels to tighten its arrangements.We have become increasingly nonchalant about our citizenship status since the UK joined the EU in 1974. EU citizenship has created such flexibility that for most UK citizens the technicalities of national citizenship law have seemed to be of little importance. But if the UK opts for Brexit the loss of EU citizenship will make it much more difficult for UK citizens to hop around Europe. For some, the simplest option will undoubtedly be to embrace their Irish-ness.Maybe it's time to call your Irish grandparent?Follow @NIconstitution for more updates on the Irish dimensions of the EU referendum.