In reply to Scarab9:
From Aer Lingus' website:
Travel between Ireland and the UK or UK Domestic travel
Citizens of Ireland and the UK must carry some form of official photo identification.
Note: In order to travel between Ireland and the UK with photo identification other than a passport, passengers must have been born in Ireland or the UK and also be a citizen of either country.
The following forms of photo identification are acceptable:
Valid Passport
Driver's licence with photo
International student card
National ID card / Government issued photo ID cards
Health Insurance cards with photo / Social security cards with photo
Bus pass with photo
Work ID with photo
Citizens of Ireland and the UK under the age of 16, do not need a photo ID, if travelling with their parent/guardian.
Citizens of countries other than Ireland and the UK must produce a valid passport and visa where applicable, for travel between Ireland and the United Kingdom.
So I am sorted for my flight from Glasgow to Dublin. Now to buy a new return flight.