From das Wiki: "Tempest will be able to fly unmanned, and use swarming technology to control drones. It will incorporate artificial intelligence deep learning and possess directed-energy weapons.[7][8]"
Really? We can't even get self driving cars right and BAE thinks we can have a fighter with lasers that controls a swarm of drones? Going to be an epic letdown when it first rolls off the line.
Unmanned does not mean self-flying. And even if it did, self driving is a much harder problem than self flying. You have rent a swarm of drones today if you wanted to.
I'm pretty sure they mean like Predator drones not your COTS hoverbots. Doing all that in a tactical/adversarial situation means the likely of catastrophic failure is high.
Air vehicles are substantially easier to make autonomous than road-borne vehicles that must intermingle with massive numbers of hazards, unpredictable circumstances, laws to abide by, life to preserve.
Airspace is, by and large, empty. For where it isn't: it's strictly controlled by other means.