Whilst I had been on the booze two nights in a row, I hope I didn't look too much of a "dodgy character" as railways suggested.

On the ID card side of things, I'm not in principle against them, I carry a EU citizens ID card from the country that I live in as my employer filled out the paperwork and paid for it, but as it's not legally required, I wouldn't have bothered had I to do the donkey-work and pay for it personally.

For Ireland and the UK however, I fail to see the benefits of ID cards above passports. There is no legal requirement to carry a form of ID at all times and there is nothing that a ID card can prove that a Passport can't. If I need to open a bank account for instance, I just make sure that I bring my passport to the bank branch. But this is an argument for another place.

Back to the topic, going by the replies, I think the border official was just confused, Irish passports are probably a novelty at the Slovenian/Croatian land border so maybe he thought I was a non-EU citizen, although I'd have thought his computer would have flagged that I was when he scanned it.