I have to go along with the crowd here and say it is the World Cup. The argument that the gap in talent is not as great in the Euro's as the World Cup is not as valid as it once was. Four or five World Cups ago some of the teams in it were very poor, I remember Canada not scoring a goal, nor coming close to scoring and El Salvador I believe getting beat 10-1. That doesn't happen any more. The teams coming out of Africa, Asia and North and Central America will be capable upsetting a number of the teams at the World Cup next year.
I also feel that climate is the key , this World Cup the climate will be favourable to England for the first time since 1966. This should be England best chance until the World Cup is held in England again, if it every is.