Comment from Eric Peterson, 16 July 2002:
Many of the links in this key are broken; I suspect that this is because it was taken from a CD for Parmelia identification produced by the BLS and they did not place the entire CD on the internet. The first species to key out does have a working link that demonstrates what is available from the CD. Contact the British Lichen Society if you want a copy of the CD. I recall that it was very reasonably priced.