The protestors are trying to stop plans by German pharmaceutical company Boehringer Ingelheim to build a European centre for research on animal vaccines on the site.
Local residents are also opposed to the idea, which would create space for 1,000 pigs for use in the vaccine tests, citing concerns about safety and possible smells.
Protesters occupied the site in July and remained for more than two weeks before they were cleared from the site. A private security company watching the densely-wooded area called police on Saturday to say the protestors were back.
Officers took around an hour to move the protestors, who were on the roof of a building and in an oak tree.