I watched the Hope video and attempted the magic 'just twist the freehub off' part. The hub is still very much attached and I have a sore wrist.
Frustration leads to the hammer which leads to having to visit my LBS with a bagfull of metal bits, so…any advice? Can I whack something in a controlled way? I have the Hope tool kit (various metal tubes and drifts).

It should just pop out, its only the seal that's holding it in.
Does the free hub not spin as it should when free wheeling?
Have you taken the drive side spacer off?

sometimes it seems to get a bit seized onto the axle. I would lever between the freehub and the hub body with a screwdriver, possibly with 2 screwdrivers to make it a more even push…

I had to spend an hour hammering the back of a cassette with a punch to get mine off. The spacer in the freehub had seized onto the axle keeping the two inboard bearings with it. It had been a looooooooong time before servicing though, its fine now.

I've had this problem a couple of times before, its normally that the outermost bearing has rusted/seized onto the axle.
If its not too bad then as sfb has said try to lever it off, or clamp the freebody carefully into a soft vice and give it a good tug.
If it is really stuck good and proper you will need to drift the axle out from the drive side to disk side with a soft hammer using something to support the wheel while providing space for the axle and one bearing to pop out, which if you have the hope tools its easy to get back in. You will see a rusty deposit on the axle that will just carefully scratch off with a penknife. HTH

As alanf says its only an o ring on the dust shield that holds its on (Im assuming its a Hope XC). Try soaking the dust shield in WD40 a bit and try and turn the dust shield on the axle, should free it up a t bit. Finally you can try 2 screwdrivers at 180 degrees to each other and try and prise it off using the freehub to lever against (there should be a narrower bit on the dust cap to get purchase on).
They can be a bit if a sod to get off.
If the obve fails try clamping the dust shield in a pair of mole grips and hit the axle end with a rubber mallet (pop a small bolt in the end of the axle to stop axle damage)

I have just had the same problem not 10 mins ago. (how weird is that)

The way i solved it is put the press on the axel and give is a little tap, as SFB says it was seazed to the axel.