For LCDMAN:
Please note that TonyV and TonyAV are not the same!
For TonyV:
It's up to individual airlines to decide what types of ID they'll accept for domestic travel (or for international travel where a passport or national identity card isn't automatically required, such as between Schengen member countries).
For UK domestic travel (and for travel between the UK and Ireland, where an 'open border' policy operates for citizens of either country), Ryanair is the only airline which requires a passport or national identity card to be produced.
All other airlines accept EU photo-style driving licences and most accept other forms of photo-ID (such as student union cards or bus passes). Some airlines also accept non-photographic forms of ID, such as pension books (which easyJet accept).