What a lively debate!
09L
What would happen at TC if one day a Heathrow Director (not
the HEATHROW DIRECTOR obviously

) was feeling a bit off and decided that they would add a bit, say a mile, to every gap?
Answer: The holds would fill up, the achieved landing rate would be looked at, the reasons for it would be sought and said Director would probably be asked to pull the finger out or be replaced.
What I am trying to discover here is, is the recommended spacing still appropriate? If it is we should all be willing to use it. If it is not, then the powers that be need to do some more work and find spacing requirements for both arivals and departures that ATC and airlines are happy to accept and then any confusion is removed.
I'm all for using common sense, but common sense, or the lack of it, varies from person to person. We should have a system that works well in normal day to day use without the necessity to resort to common sense. It is just another variable.
There's obviously something wrong with what is happening at the moment because different countries have different rules for the same problem. Who is right? No wonder pilots get confused. Is it 4 miles, 2 minutes or will 1 do?