Can you show your birth certificate - in lieu of a passport - to fly from England to Northern Ireland?

Answer 1

The answer depends on the traveller's nationality, not the origin of the flight. Regardless, most countries now require passports, and will reject birth certificates, which are not considered to be travel documents (i.e., they can identify you within your country of birth, but are useless to anyone needing proof of your identity outside your birthplace).

View the information in the related link for Ireland entry information, which may not be up to date; always consult a travel agent or local embassy or similar for current regulations and requirements.

Any airline flying from a UK airport will ask for photo ID at check in, whether UK citizens or others, and as UK citizens don't have internal ID cards, the passport is the best way of providing this, and is also the best way for foreigners to prove who they are.

Birth Certificates obviously don't have your photo as you look now, in the UK they have never had photos on them, so they would be useless. Northern Ireland is part of the UK, so if a non-UK citizen has already obtained entry into England (part of the UK) there should be no need for further entry requirements.

Birth certificates tell nothing about the person other than the information that pertained to them at the time of their birth. They tell nothing of a possible criminal record, which is, especially these days, vital information when travelling. There are many times when a person is out of jail on bail when they must surrender their passport while awaiting trial. This helps insure the person will not leave the country before their trial date, unlike a birth certificate.

Answer 2

No, you will need a passport.