The clifftop bunker was one of a number of nuclear monitoring posts, external around the UK, according to the historical research group Subterranea Brittannica.
Known as the Tunstall ROC (Royal Observer Corps) Post, it is believed to have been built in 1959 and decommissioned in the early 1990s.
Robinson and his partner, Tracy Charlton, said their YouTube channel videos of the bunker had attracted interest from all over the world.
“The story of it just captured people’s hearts,” Robinson said.
“So many people have been invested in it – it’s not just bricks and mortar, it’s something else.”
The latest footage shows the bunker sitting at the foot of the cliff, although appearing largely intact.
Robinson said that even though he knew it was going to come at some point “it was really shocking to see her just tumble down like that”.
“It was really quite emotional and sad,” he added.
Robinson said it was a “symbol of erosion in this area”, adding they would continue to document what happened going forward.