Despite zero replies I thought I'd update this in case anyone is looking for info in future.
I removed the table top. Unbolted the steel channel keel lifting assembly.
The tapered bearing was shot. I totally removed the threaded bar, it has a slight bend in it.
Ordered a new bearing (Timken A6162 - 45quid) to replace the broken one . I'm hoping this will get us into a position where we can wind the keel up again.
If not, I might see if I can get the threaded bar straightened or get a new piece.