Tourism Ireland CEO Niall Gibbons in an interview yesterday explained that under the Common Travel Area Agreement of 1923, British and Irish citizens are entitled to unrestricted travel between the two countries, simply by showing a photo ID.

Irish Ferries suggests these forms of ID in lieu of passport when traveling between Britain and Ireland:

• Photographic driving license
• International student ID card
• Government-issued photographic ID cards
• Health Insurance or social security photographic ID cards
• Photographic bus/train pass
• Workplace photographic ID
• Birth certificate for persons under 18 with no photo ID

Common Travel Area Guidance published by the UK Government states in part:

"The CTA established cooperation between respective immigration authorities enabling British and Irish citizens to move freely between, and reside in, these islands...If you are a British citizen or an Irish citizen you do not need to take any action to protect your status and rights associated with the CTA. After the UK leaves the EU, you will continue to enjoy these rights, no matter what the terms of the UK’s exit."

Membership (or not) in the European Union of either Britain or Ireland is irrelevant to the operation of the Common Travel Area.