The Irish Govt website has the following:
Rules
The Common Travel Area means that there are no passport controls in operation for Irish and UK citizens travelling between the two countries. Since 1997, some controls are in effect on arrivals in Ireland from the UK but this does not mean that you are required to carry your Irish or UK passport with you when you travel between the countries. You must, however, carry an acceptable form of photo-identification, examples of which are:
A valid passport
A driver's licence with photo
An international student card
A national ID card
A bus pass with photo
A Garda ID with photo
A work ID with photo
The Common Travel Area also involves some co-operation on matters relating to immigration issues. An alien, for example, may be refused permission to enter Ireland if it is his or her intention to travel onwards to the UK and he or she would not qualify for admission to the UK under the (Aliens Amendment) Order, 1975.
Irish Immigration Officers have the power to carry out checks on people arriving in the State from the UK and to refuse them entry to the State on the same grounds as apply to people arriving from outside the Common Travel Area. These checks are carried out selectively.
People with UK visas or residence permits
If you are a citizen of a country whose nationals need a visa to enter the State and you have a valid UK visa or residence permit, you are still required to have a valid visa before you arrive in the State. Further information about visa applications can be obtained from the Department of Foreign Affairs or from Irish embassies and consulates abroad.
Link herewith:
http://www.oasis.gov.ie/moving_count...nd_the_UK.html