Being a member of the European Union (EU), the United Kingdom's citizens are able to border cross easier within the EU. The rulings have caused much confusion to the citizens of the United Kingdom (UK) as to what type of documentation is needed when travelling to Ireland specifically.
Eliminated passport border controls were set forth by the Schengen Agreement in the EU, but the UK and Ireland are not affiliated participants.
Common Travel Area
Created by the Treaty of Amsterdam, both nations are members of the "Common Travel Area," a policy similar to the Schengen Agreement, where there are no passport controls for arriving travellers between the UK and Ireland.
Travelling out of the UK, British citizens must carry a form of official photo identification to enter Ireland.
Forms of photo identification that are acceptable include a passport, driver's license with photo, National ID card and/or government-issued photo ID cards, health insurance cards with photo affixed or Social Security cards with photo affixed to it.
Children of UK Citizens
For those under the age of 16, a photo ID is not necessary as long as the child is travelling with a parent or guardian.
Exceptions to the Official Ruling
Officially, citizens of the UK do not need a passport to enter Ireland, with the exception of any requirements stipulated by the individual ferry services and air carriers the traveller has secured passage on.