I tend to travel most from Edinburgh and generally try to get to security around 2 hours before departure. Usually travelling LCC, but the same applies for BA also. It gives me time to relax as although I enjoy flying, I find it can be quite a stressful experience at the airport in general. If I have bags to check, then I give myself another 15 minutes on top of that as there is no telling what check in will be like in that place!