Depends. Ireland & the UK are in the "Common Travel Area", which is basically a mini-Schengen passport free zone. You can land in a UK Airport after flying from

Depends. Ireland & the UK are in the "Common Travel Area", which is basically a mini-Schengen passport free zone. You can land in a UK Airport after flying from Ireland and just walk straight out without showing anyone your passport. Likewise you can drive into the UK (into Northern Ireland) and there is no border control. The only way you know you've crossed a border is the change in speed limit signs.