Peter Bowles published his autobiography "Ask Me If I'm Happy, An Actor's Life" in 2010. There are plenty of nice stories of cast and crew who would later work on Space: 1999, including a story about Val Guest's loan to Alfred Hitchcock money.
There is a brief comment about the series as marking when he changed from TV villain to comedy roles (p96)
My life in early television was about to change. I was offered and accepted the part of Balor, 'the most evil man in the universe' in an episode of Space: 1999. After playing him I knew that I could go no further in villains. I had played the ultimate. Perhaps I should turn my hand to comedy. The clouds parted and out of the blue I was offered the part of Hilary in the smash hit comedy series Rising Damp.
In the chapter "Fame and Fans" (p240-242) he mentions his encounter with a Space: 1999 fan
As I have mentioned, I played Balor, the most evil man in the universe, in the first episode of Space 1999 to be shown in America. I didn't know it had been shown when I got a phone call from the film studios where the series had been made. They said a very large parcel had arrived from America addressed to me. Would I like to come and collect it? I did. It was a parcel the size of a door (I had a lot of trouble getting it into the car) and inside the parcel was a full-length oil painting of me as Balor. There was also a charming, almost poetically written letter from a young girl studying at a well-known American university. She said she hoped I liked the painting. I had inspired her. She was studying art. She also enclosed her photograph, and she was beautiful and looked about nineteen.
At this time in the early seventies I had never had a fan letter before, let alone a painting in a parcel and I made the grave, grave error of replying to the artist at the university, giving my home address. An exchange of letters followed. Hers were always very poetical and reminded me of Sylvia Plath. Then one day I received a disturbing letter about how the other students were jealous of her talent (which judging from the painting was pretty feeble) and she had been tied up and severely beaten by them. I replied the best I could. Then came a very deranged letter, explaining that she had decided she only wanted one thing in life, which was to be my sex slave. I don't think I'd ever really heard that expression before. Anyway this time I wrote a very sensible, grown-up, married man with three children reply, saying calmly that I wouldn't be writing any more and I didn't think that she should either.
Some months later I returned home from rehearsal, and as I put the key in the door, my wife rushed to see me and explained quickly what to expect in the kitchen. There sat a middle-aged woman in some sort of tracksuit. She had blagged her way into my house by saying I had arranged to see her. She was American, she was the 'beautiful young girl' who had been writing to me, and she was obviously of disturbed mind. I had three young children in the house. I had to get her out as quickly as possible. She might have a gun or knife. I calmly suggested we should walk down to my local pub. She agreed. I showed no surprise in her appearance or deception, only in her arrival. In the inevitable explanatory conversation at the pub it transpired she was indeed at this university, that's why my letters reached her, but she worked as a waitress in the university refectory. She had a husband who was a long-distance lorry driver. He was away at the moment so she had drawn out all their money, flown over to England, booked, liked a good American, into the Hilton Hotel, and come straight to see me. She was quite adamant that the only thing she wanted in the world was to be my sex slave. The sex slave of the most evil man in the universe.
When I said, as gently as I could, that this wasn't possible, she began screaming at the top of her voice. It disturbed the pub, I can tell you. I did what I had only ever seen done in films - I gave her a quick but not hard slap in the face, and she immediately stopped screaming and let me lead her into the street. She said she was sorry for the deception and everything. She would go back to her hotel, and straight back to America. Bye, bye. Phew.
In the middle of the night there was a banging on the front door. She was back. I put on a dressing gown, grabbed keys and spoke to her on the doorstep. She had returned to her hotel, she told me, to discover an urgent message from the American embassy. Her husband had been killed in a car (or lorry) crash - but that was not all, oh no. The FBI wanted to talk to her as she had travelled here on a false passport. She couldn't go back to America. She was now all alone in the world. Could she come and live with me? I told her this time to fuck off, shut the door and went back to bed. At about 6.30 a.m. there was another banging on the door. It was short and I ignored it. When I got up I found a letter from her. It wasn't written by Sylvia Plath this time but by some cage fighter who obviously was suffering from a very serious bout of Tourette's syndrome. But anyway, the writer was on the way to the airport. I never heard from her again. I wish I'd kept her last letter, though. It was really punchy.