And for the pedants among us, the relevant definitions in the regulation are
For the purposes of this Regulation:
(a) ‘air carrier’ means an air transport undertaking with a valid
operating licence;
(b) ‘operating air carrier’ means an air carrier that performs or
intends to perform a flight under a contract with a
passenger or on behalf of another person, legal or natural,having a contract with that passenger;
Thus confirming that it is the air carrier, not the tour operator / charter company which is liable.