Which one did you write? (If you mind me asking...)
I personally find Powys interesting since they are (or were?) a very small, family-owned, independent book company, and they were(or are?) able to get writers to create stories for a prominent licensed product.
From what I understand, they have original titles by authors as well.
Lonemagpie = David McIntee. He wrote the good one.
In addition to the Space: 1999
line, Powys has also published two books based on The Prisoner
(one in a tiny run of a few hundred copies that's virtually impossible to find). I have both, but haven't gotten around to reading them yet. They have also published one non-tie-in novel.
The owner of the company is also a musician, and his band/project have published a number of recordings through Powys.