Strange light filmed flying along side a jetliner, is it a UFO?

Filmed the 15th of May on the UK coast near Marsden, this footage shows a strange light that appears to fly along side a airplane as it flies over head. The camera is relatively stable which rules out a recording glitch causing one of the marker lights to appear detached from the plane. Additionally, the swarm of flies that are in the shot don’t seem to be reflecting any light at all, making it highly unlikely one of the bugs managed to catch the sun in such a way as to create such a bright light. This leaves me wondering what exactly we are seeing in the video. Is the bright light the sun’s reflection or is the object generating the light on it’s own? Is this a UFO or something else? Feel free to share your thoughts in the comments.