....if you are from outside Ireland then you will not have a very big tax liability......in Ireland.
(My bold and addition)
The fact remains that if you are resident in the UK, or more accurately cannot prove that you are resident elsewhere, HMRC will want the difference between what you pay in Ireland and what you are liable for in the UK. If you're a 40% taxpayer here and pay 20% in Ireland HMRC will want the other 20%.
I wouldn't count on hiding under the radar either. HMRC are doing deals with the likes of Lichtenstein to get at non-payers so the Irish won't be witholding any information from them, that's for sure.