Flight Heathrow Airport departs from London Heathrow Airport at 12:35 and arrives at Athens Athens International Airport Eleftherios Venizelos at 18:20.
The flighttime is about 3h 45m. The distance travelled ("as the bird flies"): 3082 Km. So the average speed is roughly 822 Km.
There is an 2 hour time difference between London and Athens