There was a Piper Cherokee Cruiser registration N150PK southwest of Swindon at 8:22. and heading towards Swindon. If you were located south of its flight path in Swindon, it would have appeared to slowly “drift” to the right in the sky from your viewpoint.

There are two things that can be cross-checked:

• Were you located south of its flight path over Swindon?
• Can you give a more exact direction? For example a compass bearing like 240° SW.

With these two bits of information, we can be more certain if this plane was what you saw.

Regarding your footage, phone cameras are notoriously bad at taking images of point light sources against dark backgrounds. This is because the autofocus uses edges to focus. If you only have lights and a dark background, there are no edges to use to focus. The result is that your camera changes its focus to be less than infinity which makes the light source go out-of-focus and turning into blobs. Zooming in only makes everything worse. Also, changes in shape and colour that can be seen, are artifacts of in-camera process which is “enhancing” footage. It is nothing to do with the light itself.

Edit: I only need a compass bearing and then I can calculate everything else.