Removing maxi ball joint from Sierra hub?
 

The trick then? I have the hub off the car, undid the nut and... Nothing...(not that surprised!! Am guessing it's a snug fit! )

I'm guessing it has to be pushed out, but what tool do I need? or is it just a case of hammering it out with a lump hammer?

You need a ball joint splitter. Not very expensive available from just about any tool stockist.

Will that destroy the ball joint though? They are brand new, but the rubber boots have split (I've seen that replacement boots are available) so want to remove and then re fit them...

Scratch that, had a Google and discovered that splitters that aren't just big chisels are available. Thanks for the pointer!

Balljoint removers are not ideal, either, they can damage the thread and the rubber boot. Here's an alternative to try:

https://www.youtube.com/watch?v=k2HS41mJ0qA
https://www.youtube.com/watch?v=vpAwM2xH-IU

I wonder how well will this method work for our uprights with uneven manually reamed tapered holes...

My boots split too, they were rally design ones and they sent me replacements.
To split I normally loosen off the nut then put it back on finger tight. Then hit the upright/ joint with a rubber hammer. It seems to work.
My NS Tre is a problem. It spins when undoing so the only way to undo is jack the car on the track rod end. It prob isn't good for it but I can't undo it any other way.

Exactly the way I do it, never had a problem. My boots split also, they were about 4 years old without any mileage on them !!

Mine are also split, I'm going to do it the Edd China way, using 2 hammers hit the ball joint either side at the same time.