fj1. You seem smitten by the fact that Cosmos say they will be departing from Manston. That may well be the current plan. However, they aren't hog-tied to this arrangement. Try reading the small print (their Terms and Conditions):
"Although it is unlikely, we may occasionally have to change your holiday arrangements as they are made well in advance, and we reserve the right to do so. For instance, your flight details may change….
The following changes are examples of significant changes:
A change of your departure airport….."