however you need an official ID card. As UK doesn’t issue ID cards and driving licences don’t suffice, you need your passport. Some UK carriers even want your passport to fly within UK.
yes uk Ireland yes true, no visas etc and in theory no passport as a special zone. However as UK citizens don’t have ID cards they need a passport as their only form of identification to travel to Ireland. Driving licence doesn’t cover it, I’ve tried that one !