I wrote to the Goodies individually back in the '70s and received answers! My letter to Graeme was addressed to "Graham Garden" and presumably never got there, but Tim and Bill wrote back. It was sort of in keeping with their TV personae; Tim typed his letter on BBC stationary, and Bill hand-wrote his letter on orange stationary with stickers on it!
About "Graham Garden"; I had been listening to "ISIRTA" on the radio for several years and hadn't seen "The Goodies" yet (although I had heard their songs on the radio), so I didn't know there was such a name as Graeme... Sorry Graeme!