Someone’s bound to know for sure but I suspect it’s with DHL or whoever BA’s outsourced delivery to.

Usual missing luggage rules apply:

1) Make sure your address is up to date on World Tracer.
2) Do not expect any updates.
3) Do not assume BA is pulling out all the stops to get it to you. It’s probably in a huge warehouse with hundreds, if not thousands of other missing items. Like a postcard in the sorting office, at some point it’ll arrive but you can’t speed up the process.

Barring the occasional meltdown, the system’s usually reasonably efficient as long as you set your expectations accordingly. Think second class post during a strike rather than premium special delivery.