It seems to me that that SRG set up their working group to look into the "Avoiding Action" phraseology because a number of problems had been found with the original format. I believe that these were primarily:
1. Callsign clipping, thus making it hard for the subject aircraft to know whether the manoeuvre was intended for it
2. The controller issuing the correct (but somewhat long) phrase, only to be answered with something like "... sorry London, was that for us". Typical causes of this would be flight crew distraction or inattention.
The Working Group thus introduced the new "double callsign" phraseology. The bonus of this is that point 1 above ceases to be a problem as the callsign cannot be clipped and point 2 above becomes less of a problem because there is more chance that the flight crew will hear their callsign.
It seems, however, that the "double callsign" phraseology has caused some problems. I would hypothosise that one of these is that the message is now so long and includes so many numbers that flight crew are failing to identify correctly the numbers they need - usually the heading.
A possible solution to this would be to issue the avoiding action like this:
"Avoiding Action, Avoiding Action, BAW123 turn left/right immediately heading XXX degrees"
or
"Avoiding Action, Avoiding Action, BAW123 climb/descend immediately FL XXX"
I believe that the use of the words "Avoiding Action" twice would get the attention of everyone on the frequency, thereby ensuring that the subject aircraft is listening. Additionally, since less numbers are used in the phrase, there is a good chance that the correct heading/level will be taken.
Once the initial avoiding action has been given to both parties (where possible) traffic information using the clock code can then be passed.
Of course I have not seen all the research material that the working group used in coming up with their solutions, but I think that my idea has some merit and I open it up for critical analysis from fellow Ppruners or the Woking Group themselves if they are among us.
G W-H