Bittertwisted,
Here are the two relevant parts from ICAO Annex 10;
5.2.1.7.3.3.2 After contact has been established, continuous
two-way communication shall be permitted without further
identification or call until termination of the contact.
5.2.1.7.3.3.3 In order to avoid any possible confusion,
when issuing ATC clearances and reading back such clearances,
controllers and pilots shall always add the call sign of
the aircraft to which the clearance applies.
The above means that when a clearance is issued, the callsign must be included. However, the first paragraph says that the following conversation is perfectly correct;
ABC123 Seaton Control Cleared direct ZZZ FL350
Cleared direct ZZZ FL350 ABC123
Can you accept FL390
Is direct YYY available at FL390
Afirm
Roger we can accept FL390
ABC123 maintain FL350 expect further higher in 5 minutes
Maintain FL350 ABC123
--------------
I see that some on here have a pet hate of;
London ABC123 request
ABC123 pass your message
I think that while the word "request" may be incorrect, the use of "London ABC123" is perfectly correct when it is desired to confirm that the station the message is directed to is ready to receive the message;
ICAO Annex 10;
5.2.1.7.3.2.5 Communications shall commence with a call
and a reply when it is desired to establish contact, except that,
when it is certain that the station called will receive the call,
the calling station may transmit the message, without waiting
for a reply from the station called.
So if I want to say something and do not want the "Sorry I was on the telephone" response I think that "London ABC123" is very appropriate.
Since the UK publishes no difference to the above ICAO standards there is nothing wrong with their use.
Regards,
DFC