I use STN daily, but to travel by train to work in London, so see it slightly differently to those that work there. Having parked in some lonely corners of car parks at some ungodly hours of day or night, i'm not surprised at how easy it was to get airside.
I don't know if it is still true, but until recently a parking pass would let you in pretty much any car park on the site.
STN still frequently seems to be run like the shed in a field it was 20 years ago in some respects. That's not insulting anyone that might work there, just an observation.
There was a move to evict us commuters from the short stay car parks last year, and as part of the checking of tickets it was admitted that there were loads of car park passes in circulation that they had no idea who had them.
Two days (if I recall correctly) after 9/11 I reported a car in the short term car park that clearly had people living in it.....to be fair I didn't see it again after
