I'm doing a Health Psychology MSc in the UK at the moment and it is a very interesting course. However, as with every area in Psychology, the path towards working as a Health Psychologist in a hospital environment is long and full of obstacles.
Firstly, as was mentioned earlier, HP isn't really established in Ireland and HP jobs in Ireland are virtually non-existent. Your only hope would be to slot into a a job in healthcare managment maybe? I'm not too sure though.
In terms of the training involved in becoming a practicing HP in the UK it is necessary to do stage one which is a MSc in HP and then do stage 2 training which involves a minimum of two years completing various modules on research and teaching and gaining clinical experience. Unfortunately it's not as straight forward as this in reality as most people can only complete this training in conjunction with a PhD due to issues of funding, finding the experience and most importantly finding a health psychologist who is willing to supervise your training. My impression so far is that the system is very messy and the best way to go about getting the necessary training is to do a PhD, gain connections and find someone to supervise you that way.
I should also mention that there are one or two colleges (at least in London) where you can just pay (think around 4,000/year) to have a supervisor.
Sorry if that all sounds very negative!The reality is that most people who do the MSc in HP go on to work in research. Should also say that it is a very interesting area and if you are really determined and were willing to live in the UK for the foreseeable future you should go for it.
Hope that helps and doesn't put you off completely!