It is true that the UK has assigned 123.45 to ATS services.
Only the UK has done that and because it is the international chat frequency, it has published NOTAM and AIC to let pilots know.
The CAA say that the frequency is monitored!
Of course the Shannon FIR and the Paris FIR, Brest FIR, Amsterdam FIR etc have no such restriction that I am aware of and of course pilots can chat on that frequency just on the other side of the FIR boundary.
No doubt the CAA would complain about the interference from aircraft outside the UK to UK ATS facilities.
Bit of a reversal of fortunes!!!
No doubt the CAA have consulted far and wide regarding this and it will never be the case that the 121.50 speaker at Dublin ACC or Dublin Tower is turned down because of an on-going practice pan over anglsey? But is was!
Regards,
DFC