Looking at it the other way, don't forget that civil flying at Farnborough started in a fenced off enclave at Farnborough in 1989 whilst MOD test flying was still in operation.
We had remote controlled gates (operated from the control tower a mile away) to keep these civvies penned in to their own security cordon on the south side of the airfield, only opening them to allow aircraft to go in and out. This meant that if the airfield was closed, the civil traffic could not operate which rather annoyed a certain Mr R Maxwell who often wanted to just fly off somewhere on a whim at weekends so the aircraft had to moved to another airfield during these periods.
Course when we were able to extend our operating hours, this didn't matter as much and eventually when MOD flying moved out, it was a free for all with the civil operators quickly getting permission to use other parts of the airfield such as West Area.