Don't really know the regs in the UK but here in Oz there is a provision for pilot discretion in making other than mandatory calls to assist other traffic.
Standard phraseology is required in these "assisting broadcasts" so safety is not affected from that standpoint.
It is a pretty poor pilot, IMHO, who has a midair because he/she was too stuck on the minutiae of regs. I agree with tacpot that the standard should be for guidance, not as gospel.