Originally Posted by
YLU FF
Are you sure about this? I've flown from the UK to the Republic twice in the last couple of years and have had to clear customs both times. The reason is that Ireland is Schengen while the UK is not. However, this does not hold true if you fly from the UK to Northern Ireland as it is considered a domestic flight.
Ireland is not in Schengen. Ireland is in the CTA (=Common Travel Area) which consists of the UK, the Channel Islands, the Isle of Man and the Republic of Ireland.
There are limited customs controls between the UK and the Republic of Ireland, just like there are between all other EU member states. There are no Immigration controls.
The reason Ireland is not part of Schengen is that joining Schengen would mean leaving the CTA - which would mean having Immigration controls between the Republic and Northern Ireland which I think would go down like a lead balloon! As long as the UK remains outside Schengen Ireland has no choice but to stay out too.