as flightrider said....
Route swap with BA.
Longer BA Gatwick routes like Izmir, Reykjavik, Varna etc will become GB operations. A320s are much more efficient on these sectors, particularly as BA's 737-400s are payload limited on the return ADB-LGW sectors etc and have limitations on payload on KEF due to diversion alternates.
In return, short GB routes like Nantes and Montpellier will move to BA in return. BA can also use 737-500s on these routes to grow flight frequency and maintain year-round service which is not viable with the A320.
One set of LHR slots to be sold to BA. Double-daily Malaga and single Casablanca to be maintained, the daily LHR/Faro will disappear and be replaced with an extra frequency ex LGW.