Haroon
The term "separation" is somewhat relative when used with air traffic advisory service because this service will not issue clearances, it will only give advice and suggestions. Needless to say, separation based on such suggestions can only be achieved between aircraft which are known to the unit providing them. In other words, aircraft which are not "participating" cannot be separated. Keep in mind that ICAO permits IFR flights in airspace class F without clearance, so in airspace class F there might be a wild mix of IFR and VFR flights known or unknown to the air traffic services unit in charge.
As for your question concerning universal or European application of the respective rules, each state will have its own rules, some do not even have class F airspace (Denmark and Chile if I'm not mistaken), others might not provide air traffic advisory service at all but offer flight information service instead. Here in Germany, for example, IFR flights in airspace class F are subject to an ATC clearance and there will never be more than one IFR flight at the same time in the same airspace.
Last edited by hvogt; 26th Jul 2013 at 06:58.
Reason: typo