The RSPB web site has plenty of bird feeders with peanuts. So does our local Pet shop, come to that. I stopped using them because it is impossible to find anywhere to hang them that the squirrels can't get to.
I have to admit I was a little dubious about the squirrel getting access to the air filter, and unfortunately the paper with the story in has now gone for re-cycling so I can't remember if it gave any technical details. Maybe Dave would fill us in.
FC