I was in that position myself about 10 years ago so I understand your dilemma. When I bought, I made a few mistakes, and if I was doing it again I would do it differently. But in spite of that, I am much better off now than had I not invested.
I am reluctant to give advice as everyone's circumstances are different but if I was in your shoes, I would do the following.
1) Only invest what you can afford to lock away for at least 10-15 years.
2) Pay off your mortgage and max out your pension before you invest in an ETF.
3) Pick a broker and open an account. There are lots of good ones - just do a bit of research here on AAM.
4) Pick an Accumulating ETF which tracks a large index of your choice. Do a bit of research to make sure it is UCITs compliant using this
link .
5) Buy one single ETF in one single transaction. That will make deemed disposal a doddle later on.
6) Register for ROS and do a form 11 every year from now on. The purpose of this is to declare what you have purchased and, in time, pay the tax due on deemed or actual disposal. Doing form 11 is also not that hard and most of it will be already prepopulated if you are PAYE.
Once you have done that, you have the next 8 years to figure out the deemed disposal but it's not that hard especially if you only have a single transaction.
Best of luck...