Has anyone experienced the clock and trip computer resetting for no apparent reason on a mk3 Octavia? Or does anyone know what could cause this?

I don't know if any other features are also affected but the clock and trip comp are the most obvious.

Any hints or ideas to check would be much appreciated.

p.s. counting back from when the clock reset, I know that whatever caused the event, it happened when I parked and switched off the car.

I had this problem about 18 months ago.  The trip meter went back to zero and the clock reset itself to 00.00.  Also sometimes the clock showed the wrong time until I started up the car when it corrected itself.  The Skoda dealer said they re-installed the software but the clock showing the wrong time problem is still there.  I can't be bothered taking it back again so just live with this problem. 

This is symptomatic of a falling battery.  Get the battery checked out and check the SOC (state of charge) to see what the battery is doing.