WH, the Home Secs comments shed light on why the restrictions applied to GA only (actually to all a/c not operated under an AOC if I remember). I'm not getting into a debate about the rights and wrongs of the action, and it was only for a short time, but it didn't ban GA. Reference to the Notams showed that flights could be made, but had to be registered and have permission first. There were (from memory) three telephone numbers given in the Notam to request this permission, so it looks to me as if they had allocated considerable resources to dealing with these requests. I didn't need to telephone because the restrictions were quickly lifted. My guess (only a guess) is that if your aircraft was based somewhere like Birmingham Int which has tight security, it would have been very easy to get this permission. Similarly, I expect IFR flights would be have been easier than VFR.
Thank goodness it was only for a short time.