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Join Date: Feb 2009
Location: From ORK, live LCY
Programs: BA Silver, EI Silver, HH Gold, BW Gold, ABP, Seigneur des Horaires des Mucci
Posts: 14,237
On an LHR-DUB Aer Lingus will accept various identification including student cards, bus passes, work ID etc.
INIS (Irish Naturalisation and Immigration Service) will be less willing to do so. A driving licence with a place of birth in the UK or Ireland will generally satisfy them, as will a reasonably genuine looking photo ID accompanied by a UK/Irish birth certificate. (This is still the case despite the fact that since 1/1/1983 being born in the UK does not by default give you citizenship.)
If you can't produce something along these lines, you may be delayed at the border. If you have been before they will probably eventually find you on the system and let you through, but expect to be told off and advised to "bring proper ID next time".
On DUB-LHR there is no passport control upon arrival so there are no issues.