Hi Ian,
I believe that ID is a positioning one.  I have seen it on occasions, once out of Newcastle for example when one of the fleet went out into the North Sea for a flight test and back.  
It may well have operated the first of a series from somewhere to Ibiza and has no passengers for the return flight and could be operating a flight out of LEAL in the morning back to the UK and positioned over from Ibiza.
Alan