The application was initially refused because the site is green belt land on a major road that will be dangerous for likely protests. That decision was upheld by a public inquiry. It was approved by John Prescott's office because "it is strongly in the national interest," there is a lack of superior alternative sites and the site is already authorised for animal research. A letter from Lord Sainsbury to the inquiry reaffirmed this government's support for animal research and stated that this centre is necessary for the UK to be a "global leader" in neuroscience and "strengthen Cambridge's role in leading edge research".
The secretary of state writes that concerns about protests can be ignored because "risk of unlawful activity should not dictate policy." He also notes that the location on a main link road between the city centre and the motorway is an ideal location for protesters, but says that "effective policing methods" will keep them under control. His decision can only be challenged in the High Court in limited circumstances.
This 28 page letter is on the ODPM planning page as a PDF under a bland title. There are news releases from S Cambs DC about this decision and their original decision. Cambridge University issued a PVC statement. Bidwells are acting as agents for Cambridge University in the development, but have apparently published no statement. They also manage the Science Park.