Aliens have invaded Bristol! Yes, you heard me, Bristol. In the UK. Why? Maybe their ship was damaged. Lost navigation or something. Probably were originally planning to invade New York for the millionth time. You've got to feel for them. Bristol!
Anyway, if you really want to know why, then I suggest you head over to a new SF web series called Horizon. The first two episodes are already released with the remaining eight being made available daily at 8pm GMT.