You seem to be hanging your hat on this one bit of video as irrefutable proof there was a drone flying over Gatwick without conceding the possibility that it could have been easily fabricated. I have seen far too many much more complex clips later revealed as frauds. The lack of official acknowledgement of this footage as genuine is highly suspicious to me. They are investigating “Reports From Witnesses”. Also that the thousands stranded, the authorities, ground crews, pilots, tower personnel, etc. have not produced a single, credible image is beyond amazing. Generally, the public cannot wait to Twitter, Instagram, Facebook, email and text every visual facet of their lives. But NO DRONE PICTURES
Okay - so you are proposing that the video was faked. I guess that's the standard response these days to unwelcome news. So far we have (1) it could have been taken elsewhere [disproved], (2) it could have been taken at some other time [problematic in itself] and (3) it's fake.
And no - "evidence" and "irrefutable proof" are quite different concepts, even though the "prove it" fallacy is often deployed against evidence. The video corroborates the multiple reported sightings. It seems like strong supporting evidence.