In 1991 and 1992 when we had European finals taking place at Wembley it started off with Italian and Spanish flights using separate airports but in the end they both used Luton and Stansted - of course the UK was a different place then and not essentially a police state as it is now - cameras and signs everywhere telling what you can and cannot do - it is first thing that hits you as you step out of the arrivals hall after you have flown in from abroad plus the traffic as well of course.
Many aircraft did not stay overnight and that was when it was played on a Wednesday and there was plenty of parking. The cargo area at Luton was used as a bus park!
In Euro 96 many German supporters flew over so we will just have to wait and see plus the large amount of corporate traffic whoever gets to the final.