For events occurring within its temporal scope, the Montreal Convention is the overriding authority, taking precedence over domestic legislation and contractual terms. There is plenty of case law to support this, not only in the UK but in other jurisdictions.
I am really getting confused now, I thought you were proposing to claim under s75 of the CCA 1974 and include a request for consequential losses resulting from the supposed breach?
Does the Montreal Convention say if your flight is cancelled you can take action against the cancelling airline to recover all loses from the trip including separately booked flights and other expenses associated with that separate booking?
A straight answer to a straight question would be appreciated please