If I'm driving in stop start traffic and slip it into neutral to coast up to the car in front of me, the idle speed stays at 1200 until the car comes to a complete stop, then it drops to 800. It's 11 years old and has always done this so I'm not bothered by it. I just wondered what the reasoning is behind this particular trait and do all Octavias do it?

I think the switch on the clutch pedal changes the way the revs drop when you take your foot off the accelerator,depending if you are just lifting off to slow down or if you have the clutch depressed to change gear.

Switch could be faulty or the throttle body might need cleaned and aligned.

If I'm driving in stop start traffic and slip it into neutral to coast up to the car in front of me, the idle speed stays at 1200 until the car comes to a complete stop, then it drops to 800. It's 11 years old and has always done this so I'm not bothered by it. I just wondered what the reasoning is behind this particular trait and do all Octavias do it?

as far as I am aware it is normal it will drop down when you stop,it is a saftey so the car won't stall there is a sensor on the fly wheel that reads your speed....

All modern cars do it as said above i think its a safety feature. Autos do it all the more

Higher revs allows easier engagement of first gear, like when you are approaching a roundabout and need to be able to act quickly.

When you are stationary, you don't need these extra revs, so it drops back down to the normal idle speed.