Cows getting bigger.
The field sites were strictly peactime training sites aimed at making the training case harder than the operational case. The war sites were supermarket car parks and other urban areas. (less mud and some general IR all round. The IR signiture of a field site was silly!)
Interestingly if the whole thing went really wrong the Harriers were the only aeroplanes that you could take to where the fuel and/or weapons were stuck behind the lines.