Right-o gents, good news and bad news.
Good news is I've managed to change the resistor pack without removing the dashboard, bad news is it's f-ing fiddly to do (took me about an hour to do and some of it will be done blind by feel alone).
I can't post links or upload attachments so I've just embedded the images from the image upload site I used - so they might disappear at any time...
Read through the step-by-step below first and then follow the instructions at your own risk (if you've got really big hands or aren't nimble fingered it might be too tricky, see the last picture for the state of my hand at the end).
First you're going to need some Torx bits (according to my bit set it's a T-20) and a knife or scissors to cut the soundproofing insulation with.
Step 1 - Remove the glovebox (the easy bit).
Unscrew all of the screws circled in red both in the glovebox and underneath (ignore the loose wire that's for my dashcam). I didn't have to do anything to the pegs circled in green (the glovebox just pulled out), but you might have to press the central bit in with a screwdriver or something. Pull out the glovebox,
be warned the airbag switch is still connected, I managed to get away with doing the job without disconnecting it.
Step 2 - Get access to the pack
The resistor pack is located roughly where the red circle is so you'll either need to remove the white sound insulation material or cut it along the green lines -
be very careful as there are a lot of wiring looms around you really really don't want to cut those!
Step 3 - Locate and remove the pack
Now the fiddly stuff begins. The resistor pack is located where the red circle is behind a lot of wiring, you'll have to work around these cables, underneath and/or over the top. To remove the pack you'll need to give it an anti-clockwise twist, that will unlock it, then you'll need to turn it a bit more and then lift upwards to get it out.
Step 4 - Unclip the resistor pack cable and replace
There are toggle clips either side of the plug circled in red, press them inwards and pull-out the plug (remember how it was positioned and connected). Once that is done you can remove the resistor pack. This is where it might get even more fiddly, partially put the new pack back in and then reconnect the plug (it should only go in one way) - it could take several goes and you might need to find the resistor pack position that works best for yourself. Once plugged in put the resistor pack back in place and give a clockwise twist.
Step 5 - Put everything back.
Put all the wiring back in the correct place if you moved, put the sound insulation back. Put the glovebox back it place, there's a white clip at the bottom of the passenger foot-well make sure the bottom of the glovebox gets slotted in there. Put the screws back and push-in those pegs (they didn't snap into place for me).
Survey any damage to yourself, if you want an idea of how fiddly this is this is my hand at the end.