I've taken a look at all the Friends of the Earth group accounts I follow, as well as individual accounts by people involved in Friends of the Earth local groups (minus those who mainly tweet about non-environmental issues).
I then correlated the most frequent tweeters and the most followed to compile the list below.
This isn't any kind of official list - and of course many of the individual accounts tweet about other interests and affiliations.
But if you're looking to connect with the most active corner of the Friends of the Earth twittersphere then follow these people. :-)
Here we go - in no particular order