Case of mistaken identity? Not Harriers but Czech Air Force Aero L-159A ALCAs. They are currently on exercise and operating out of RAF Leeming.
First link is taken at Leeming and shows the tanks carried.
Aero L-159A ALCA (6066) Aircraft Pictures & Photos - AirTeamImages.com
Photos: Aero L-159T1 ALCA Aircraft Pictures | Airliners.net