the new NATS ammendment associating to degrees is for the word to be used mandatory for headings ending in zero, and only advised for any others.
Why isn't FL500 a separated level??? Again in the UK, as there is soo little up there anyway it can be used so long as all other a/c are given the standard 2000ft separation, or 4000ft if supersonic. It wouldn't affect the military either as it'll have to be co-ordinated due to it being above FL450.