In the incredible clip, a dark, wispy figure can be seen slowly walking across the entrance at Dover Castle in Kent before disappearing.
A bemused security guard can then be seen searching in vain for the mysterious spectre.
The one minute, 11 second clip was uploaded to YouTube by a user known only as spyder1spanner2.
A message accompanying the post read: “I promise you this is not a fake.
"It’s filmed on CCTV at Dover Castle on to a mobile.