Been away for a few days but I note the same argument is still going round and round!
The main issue seems to be not one of frequency clutter but of a perceived lack of integrity of a student pilot who might wish to confirm his position by using an established procedure!
I flew 24 sectors over the last three days. We heard one practice PAN from a Coventry student who correctly used the facility for a position fix from D&D. However, on every sector we heard a number of airline pilots incorrectly calling on 121.5, mostly inadvertent, some of them answered by other pilots, some of them by D&D.
However, the most blatant, almost unbelievable example of misuse we heard occurred this morning. A "Speedbird" callsign (I have the flight number) made contact on 121.5 then called a company callsign over to 123.45.
This goes against the CAA mandate (NOTAM'ed) that the latter frequency is NOT to be used in UK airspace for air to air informal use as it is allocated to at least one authorised user.
We followed them over to that frequency out of curiosity and were amazed and apalled to hear a two way chat about where someone's wife was going today (it was Amsterdam, apparently).
The integrity of students is the least of our worries if so-called professionals are doing this sort of thing.
BTW Beagle, Don't forget that the RAF's training procedures were designed for the use of 243.0 MHz, not 121.5, so it is irrelevant to the argument!