Yes. You can increase your baggage allowance on 20kg bags when you check in for your flight online. Passengers can add up to 3kg in excess baggage to each 20kg Check-in Bag for a fee when checking in online, up to 2 hours before departure.
Excess baggage options are unavailable to be purchased online on flights departing from certain airports, included but not limited to Milan Bergamo, Birmingham, Bologna, Bristol, Cardiff, Dublin, Edinburgh, Krakow, Leeds Bradford, Manchester, Naples, Newcastle, London Stansted. If you are departing from any of these airports and need to purchase excess baggage allowance, you can do so at the airport check-in desk.