FlyLowCost
This is the problem with taken the top 50 airport pairs and trying to derive the top 10 city pairs from that list.
In fact the total London - Milan in terms of passengers in 2003 was: 1,928,930 of which 1,913,809 were on scheduled flights and 15,121 were on charter flights.
If you've got time see if you can come up with the definitive city-pair listing!