I assume this is the same cave that someone told me about that could hold so many hundred people. I can’t say I have seen this feature but it is likely to be completely natural. There is no evidence of any top entrance as can be seen at Marshall Meadows (see previous post). The boulder is likely to have been jammed in by wave action. I always ask, “If it were man-made, why would anyone do such a thing?” The effort of getting a large boulder up into the cave sounds like a lot of effort for what return?
That the cave is natural is supported by Fuller in his History of Berwick (1799). He talks on p471 of the Pigeons Cave (interesting that you were looking for rock doves!) which “has been excavated by the waves of the sea, and appears capable of holding 1000 men.
"There are two other caves nearer the town; one of them is called Burgesses Cove and the other the Singing Cove.”
His caves and coves may have got misprinted!
Thanks for bringing it to my attention – I must pop down to have a look sometime.