I will visit London the day after tomorrow and i will stay for four days then i will go to Athens for 2 days. can i go from Athens (Greece) to Milan ( Italy ) by plan to spend another 7 days in Italy ........ I have a Schengen Visa (c visa) single entry valid for 10 days issued from the Greek consulate and one my friends told me that i can not travel by plan from Greece to Italy because this will make leave the Schengen territory is this true and what i have to do to enter Italy from Greece

When you fly between Italy and Greece, you remain in the Schengen area and you do not cross any external border. Therefore, a one-entry visa is sufficient for your trip.

Where are you now? What is your nationality?