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HappyJohnUK
Even if both LGW and SXF were open Easyjet can, as far as I am aware, still claim
force majeure if they had to cancel flights because aircraft were stuck at other airports... so you really need to find out the
precise reason for the cancellation.
One way to find out is to enter your flight details here:
http://www.euclaim.co.uk/Calculator.aspx