The following introduction is taken from http://citizensinformation.ie/catego...thern-ireland/
If you are currently living in Ireland and thinking of doing a third level course in Northern Ireland (NI) or elsewhere in the United Kingdom (UK) there is a very wide range of courses available. Many people choose to study in the UK because a particular course is not available in Ireland or because the entry requirements are easier. Others want to have the experience of studying outside Ireland. Before you apply you should find out about the different structures and costs for third level education in the UK (pdf), in particular fees and living costs. For example, there are different fee arrangements within the UK. The United Kingdom (UK) includes England, Wales, Scotland and Northern Ireland.
Most UK undergraduate courses last 3 years but in Scotland they last 4 years. In addition the application process starts earlier than in Ireland. This means you should begin looking at courses at least 12 months before you plan to start studying. The application procedure for all UK undergraduate courses is the same (see below for further details).
Important dates: http://www.ucas.ac.uk/students/importantdates