No big secret on on how Peel got the role. I asked the producer Anthony Hinds, and he said he had seen Peel on a television program I believe, then contacted Terence Fisher about it. Heck, let me check the issue...
"I saw him in something on television and phoned Terry Fisher and asked him to watch the repeat. He (Peel) was a nice chap and we got on well, but were never really friendly."