I've got the right tool which I've been wacking with a lump hammer. As from the pic below, I have even got a wedge (tyre lever) in from the top to try and help out. It still doesn't want to come out. I've rotated the driveshaft a number of times, and re-tried shifting it, but still no luck.

This pic shows as above, but with the proper tool in place. I have been hitting the tool hard (on the large flat surfaces) with a lump hammer (I'm working on my garage floor, not in a pit or on ramps unfortunately) and it just doesn't want to split.

Two questions.
1. Any other suggestions on how to shift it using the current method?
2. If still no luck, will undoing the four blots around the pot joint area of the gearbox be an alternative solution (without messing about with the gearbox in a big way).
This is a 998cc Auto Mini by the way. 1983ish.