Andy, in November, the flights from Gatwick are at 8:30 on Saturdays and arrive at Almería airport at 12:15. Perhaps there will be flights from Gatwick in January on Tuesdays, Thursdays and Saturdays.
Another possibility is to fly from Gatwick to Murcia airport with Monarch. It leaves at 7:45 and arrives in Murcia at 11.15.
http://WWW.flymonarch.com or go to Alicante or Málaga with Easyjet from Gatwick. Then you could rent a car and leave it in Almería and return from Almería to London Stansted or return to Gatwick from Murcia airport.
There´s also the possiblity of coming from Gatwick to Almería via Madrid or Barcelona with edreams but it takes longer and it is more expensive.
Best of luck
Antonio