Some terms and conditions which are worth noting since it seems unlikely that if you do not actually take the seat in most cases the amount paid is lost:

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British Airways has the sole discretion to determine whether a passenger meets the requirements to sit in an exit row seat. If the passenger does not meet the requirements, they will be assigned an alternative seat. The additional amount paid for an exit row seat will be forfeited and will not be refunded.
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Exit rows purchased through Online Check In will not be refunded if you are unable to fulfil the requirements to sit in an exit row.
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Paid seating will not be refunded if you cancel your flight, are involuntarily upgraded or are not suitable to sit in the seat type you have selected.
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In relation to BA marketed and operated flights, if, in accordance with your fare rules, you choose to move to a different flight, you will be entitled to choose an equivalent seat on your new flight. However if an equivalent seat is not available the difference paid will be forfeited and will not be refunded. In relation to other carrier marketed flights, if you choose to move to a different flight, you will not be entitled to choose an equivalent seat on the new flight and you will not be entitled to a refund.
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