I was outside my work taking the bins out one night, i decided to have a smoke so stood there looking at the sky and noticed a flashing green light in the sky and didn't think much of it until i realised it wasn't moving. it seemed plane height so roughly 30 odd thousand feet. and then the light got brighter and it seemed as though it came close towards me. at this point it was above a building and then two lights start flashing. the flashes were a few seconds apart and the the light/craft starts darting and zig zagging in the sky and descending slowly and ascending quickly. my friend who was with me thought it was a drone or something but it was far too quick to be a drone and there was zero noise through out the experience. after a minute or so it vanished but shortly returned this time flashing red. i managed to get a short video of it but i wish i got my phone out sooner to get the whole thing