This had been discussed on a-n-other forum before GA was around and someone contacted the CAA about it.
Their response was that it was ok to post videos on YT and receive advertising revenue
Whilst every case should be judged on its own merits, some types of arrangements are not generally considered by the CAA to be aerial work:
Advertising revenue received as a result of persons visiting a website or social media page where video or photographic stills shot from a drone are displayed/posted. This is because these types of web-pages may be legitimately used to post recreational video material that was not commissioned by another party, but was conceived and wholly funded by the poster. This would not apply if the photographic material had been directly commissioned by another party for the purposes of display or marketing on their website.
See section 11. in the attached PDF from the CAA
Drones.pdf (514.1 KB)