For what its worth, in the US:
Heli Air 2 Air = 123.02 is used frequently amongst copter operators, particularly the 'news' copter operators. Even the military helos will come up on that freq., when passing throught the area. In fact, I would usually monitor this freq., when I could. I couldn't imagine not having a heli-air-2-air. But I guess (but may be wrong), in the UK you are under more AT control, so 'self-announce' procedures are not used as much??
FW Air 2 Air = 122.75 - Not used often...in fact have never been able to get anyone on this!! Nevertheless, the freq., is reserved for that purpose.
cl12pv2s