Actually it goes all the way back to Supercar! There are several photos from various Anderson shows on Master Models' current website. They also made the Zero-X miniatures for the Thunderbirds feature.
AP Films/Century21 had their own model shop at the studios, but would often farm out models when the workload was too high, particularly when a new series was ramping up. That's why many of the key hero models were made by these companies. Space Models was started up in the mid-sixties by several staff from Master Models, so many of the craft were made by the same people. The late Arthur 'Wag' Evans is credited with building the hero models of Stingray, Thunderbird 2 and 4, the puppet-scale Fab 1, and the three initial Eagles (44", 22", and 11") for Space:1999. He was still at the company in the early 90's, so might well have been involved with the Blake's 7 models.