Along with UK, Ireland is a member of the Common Travel Area. Thus, British citizens do not require a visa, or a passport, in order to travel to Ireland. However, it is strongly advised that British nationals still carry their valid passports with them whenever they travel to Ireland as Irish immigration officers will check the photographic identification of all travelers arriving by air from the UK.
Other types of photographic ID may be acceptable for some carriers and the Irish immigration. British travelers are advised to consult their airlines beforehand and heed any advice given to them.
For further information on what exactly will be required of a British passport holder at immigration, please contact:
Embassy of Ireland
17 Grosvenor Place
Telephone: (44 20) 7235-2171
Fax: (44 20) 7201-2515