Don't count on the quick access for closing flights always working - depends on the airline informing the security manager of missing pax. I have observed people missing flights at LCY due to security delays. Not a pleasant thing given the lack of frequency on many routes.

Having said that, if the people who run LCY put half as much effort into managing their security staff and having the appropriate level of staffing as they put into facilitating queue-jumping [people with flights about to depart/families] we would not have this problem.