I have every sympathy with both the student and GA pilot using 121.5 to save their lives. I have trained many to use it without hesitation. I taught PPLs at EGCW and we refered to 121.5 as "EGCW Radar" - being hard to find anyway and churning out 60 PPLs a year we were one of their biggest customers!
And yet. The current situation is that on many days many airliners are turning 121.5 down to nothing because of the high levels of GA use. They then forget to turn them up again 5 minutes later. There are several ways of tackling this flight safety hazard. My preferance would be to invest in a 121.4 solely for GA use in the UK airspace offering a dedicated D&D service.
Cheers
WWW