It's called continual improvement except this is the first building work to the passenger infrastructure for a few years so I don't know what you are talking about when you say a building site since the 1980's.
With respect, continual improvement that has led to no improvement is not progress. The proof of no improvement is that 30 odd years on, it's still a building site that the travelling public have to endure each time they travel through it. I appreciate it is very difficult to improve and enhance any structure whilst it's open to the public, but 30 years !! Come on LTN, make these latest "improvements" the last and build an airport all can be proud of.