Have often thought that there should be an "unofficial" convention on altitudes around the London airspace ..........often get opposite direction traffic at the same level no matter what altitude ...........
I'm talking about flying around the London CTR class A, underneath the LTMA especially where squeezed by other airspace. It wouldn't cater for all flight headings but a suggestion would be to fly Clockwise =EVENS ( 1200,1400 ,1600 etc, Anti-clockwise = ODDS ( 1300,1500,1700 etc )
What do you think ???