Whenever you can try to avoid flying Air France. I flew 3 times with Air France and 2 of them were disasters. Flights cancelled, no refund, arrogant staff. I had to take the Eurostar from Paris to London since Air France cancelled the flight, allegedly due to weather conditions in London (which was a lie). I never got any refund from them. Nobody even picked up the service hotline - so what's the point of having it?! If you want to get to your destination then avoid Air France at all costs. There are much better 'budget' airlines that fly to France from the UK, either that or take the Eurostar.