Oceanrower, not trying to start a flame war, but attaching ropes to the fence posts was one of the main reasons leading to the ban on climbing/caving on this bit of cliff (or at least to the top of it). For info the fence posts are set into the earth glacis of the old fort. This bank of earth is apparently structurally important for the fort and frequent attachment of ropes was starting to make some of the posts wobble and so damaging the glacis. This was along with the problems of ropes across the footpath on the cliff edge and various other antisocial behaviour by a few.
As previously noted, all of the anchors on the cliff edge have been chopped. As to climbing up, I am sure it could be done. However, I suspect that it would be much simpler to climb to Queen's Entrance rather than Main Entrance. There are (to my knowledge) no anchors at QE, but you could always exit via Main Entrance using the anchors there for a retrievable abseil.
As to climbing back up from Sandy Hole. It is possible to get up Squezy Rift, indeed this was the only option prior to the linking of the two caves. It is naffing strenuous though and more importantly will inevitably drag a lot of mud up into Blacknor Hole, which for the most part is pretty clean (at least compared to Sandy Hole).
If the ownership of the Fort has changed, then we have an opportunity to regain access to an unusual cave, and fine sporting trip - so long as no-one upsets the landowner before negotiaions can even start! Tread carefully please.