On the topic of ID cards:
I'm a dual Polish/British citizen, and I went to Ireland last month via the UK in both directions because of the lack of direct flights. I had quite an adventure with my Polish ID card:
- mandatory use of the Polish ID card to leave Poland.
- ID card used for boarding, with a cursory question ("are you resident in the UK?). I lied and said yes, out of idle curiosity.
- Presented my ID card at Luton, and the bloke at immigration was confused when he couldn't find me in the database. I played stupid by pretending not to know the rules, and then he figured out that I was probably a British citizen from the name and accent. He asked (very nicely, I must add) if I had my British passport on me, which I did. If I didn't have it, he said that they could still admit me, but that they'd need to get his boss to verify that I was a British citizen by checking some database that he didn't have access to.
- Polish ID used when boarding in Luton
- Polish ID used on arrival in Dublin. Quite shockingly, the Garda officer on arrival there assumed that I was there to work/was working, and she started a conversation about this! We had a laugh about it, but in hindsight: she wouldn't have asked that if I used my CTA rights. I thought about using my CTA rights by handing over my Polish driving licence which clearly states that I was born in the UK, but I wanted to get to the pub.
- Polish ID card denied for travel to the UK from Dublin (!). The agent claimed that they weren't acceptable, and even when I told her I was a dual citizen, she demanded to see a passport.
- no check on arrival in the UK.
- Polish ID card used for departure from Standard
- Polish ID used when arriving in Poland.
No idea why UK citizens weren't questioned upon entering Schengen, but it seems like it was already allowed/possible.
This was largely down to the UK not really complying with the spirit of FoM. Although, as a British citizen, I was definitely asked a few questions in the past, especially on the Slovenian-Croatian border.
Oh and on ID cards - the UK has long not liked them so has not stopped accepting them as is in its gift with Brexit
Much to my annoyance. It's so much easier to carry a plastic card than a booklet!
My understanding is however that the UK chose not to accept them because the level of forged ID cards is much higher than for passports.
The key issue here was that some EU countries (specifically Italy) had major issues with phasing out paper ID cards, and the EU was unwilling to let the UK only accept biometric ID cards. It could have been negotiated, but the UK didn't show any real interest in the topic. As it stands, it's still perfectly possible to fly into Ireland with an ID card, and then travel onwards to the UK without encountering any control and all with a standard ID card. My experience in Dublin Airport seems to have been the exception rather than the norm.
Even EU citizens are not guaranteed entry into Ireland.
Not guaranteed entry, but in practice, it's very difficult for Ireland to block an EU citizen from entering Ireland. It can only be done in very limited circumstance, and 'intent to breach UK immigration law' is not one of them.
Ryanair insists on a passport as ID to board.
EEA ID card is enough for UK-Ireland flights and reverse.
The checks the passport officers have to do if you're entering the EU are not quick, it's far more than just stamping the passport. Takes at least five minutes per person once all the questions about length of stay have been answered, existing passport stamps are checked and calculated alongside the usual scanning process.
This is not the case on most borders. I quite routinely travel using my British passport across the Schengen border, and very few countries bother with interrogating British citizens. Spain was one of the exceptions, but in general, they usually just stamp my passport after flicking through it. I have my Polish ID as a backup in case they whine about the stamps/overstays, although my passport (according to the stamps) normally shows that I'm in no man's land somewhere. I just checked, and currently, my passport thinks that I'm stuck on the Croatian/Slovenian border as I deliberately got stamped out of Croatia and then used my ID card to enter Slovenia.
Even with the new arrangements, it's not going to take more than a couple of minutes for most travellers.