Cause you can. But...There is no baggage allowance associated with the purchase of an extra seat.
''If a passenger wishes to purchase an extra seat (whether that seat is needed for additional comfort, a musical instrument or other items), that customer will have to pay for the additional seat...Please note that extra seats cannot be purchased for infants.
Passengers can purchase an extra seat online by entering the passenger name for the additional seat as Mr EXTRA SEAT. Alternatively you can contact our reservations department to do this.
Large musical instruments such as harps or double bass cannot be carried in the cabin of an aircraft. Other musical items such as a guitar, cello, violin or viola which exceed our cabin baggage dimensions may be carried in the cabin if a seat for it has been reserved and the appropriate fare paid.
If you have purchased two seats please arrive at the departure gate at least 30 minutes prior to the scheduled flight departure time. If you are unable to locate two seats together on the aircraft please contact our cabin crew as they will be in a position to ensure that you have two seats together.
Online check-in is not available when a extra seat has been purchased.''
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