I have an 2006 1.4 tdci Ghia that of course comes with a few toys.  I have had issues over the past few weeks with the battery going flat despite both the battery cranking power and alternator checking out fine with an analyser.  As it is running fine once jump started, it must be battery as opposed to alternator related.  

Without really thinking I bought a new battery as I did not know its age.  Upon removing the old battery and with nothing turned on in the car there was a distinct spark and the remote door locks activated as I remover the first terminal.  This I perhaps indicates a parasitic loss via the locking system(or elsewhere). 

How do I go about delving deeper into this issue and are there any components in this area that are known to fail?

I one had an issue with the driver's door lock. The lock contains the "door open/door closed" micro switch. It was faulty so kept activating the interior lights on me. It was obvious though even when you were present in the car as you would lock the doors from inside and they would spring open again on the handles or if be driving and the interior lights would all come on and the note on the dash would be constantly on saying door open. Got very annoying so replaced the doorlock with a used breakers part and never had another issue. It caught me out for battery power a few times though for sure.

Should anyone read this in the future with a similar problem.......  Despite the battery being tested by a car accessary shop as being fine, I eventually replaced the battery and have had no similar issues since. Lesson learned!