My heart goes out to you folks in the UK. You don't have a fighting chance should tyranny and further oppression come down on you. But that is thread drift. If your little pop gun is accurate and you are a deadeye shot, any head shot should do the trick. Hey, do they let you have bows and arrows over there? Wrist rockets? Slingshots?

If not you can frame a greehouse from PVC pipe and put in raised beds. Do they let you have PVC pipe? Glue? Sharp objects of any kind? Maybe you can get an MP to come and talk the birds to death.