Of course there's information on the revenue website and on citizen's advice and presumably on UK revenue's site. Most of us wouldn't know about the UK, but firstly I imagine tax has to be paid there and this will be credited against any Irish liabilities.
Are we talking about a lot of money?
Because this is Ireland/UK most solicitors will surely have some experience of dealing with this situation, you need to find one of those, especially if the amount is large.