Sorry for not responding to this sooner, I hadn't noticed the thread had been updated.
I haven't filed an airprox report - I am concerned that my memory of the details is somewhat sketchy due to my being focused on whether or not I had drifted and infringed into a DZ.
I do now have a GPS receiver and SkyDemon to use with my smartphone, but at the moment I am only using it as a post-flight debrief tool (to compare my actual track with the one I planned and think I've flown) and for emergencies when I am absolutely desperately lost. I have it running but don't normally refer to in flight. Even in cases where I am uncertain of position I'd rather get into the habit of putting the airplane into an orbit and getting a fix from nav-aids, asking ATC for help etc. I am hour building to prepare for CPL and I'm assuming that on the skills test the examiner won't accept my Android device as evidence I know how to employ the proper lost procedure!
Many thanks to those who have shared details of previous incidents involving drops, it's definitely eye-opening.