Once you've got the rotory switch out, it's time for a little violence!
The switch is practically a sealed unit, and I was looking how to take it apart while still being reliable after reconstruction... the short answer is that there's no real way to do it - if you force the case open it'll never go back together properly again.
Solution! You'll notice on once side there's an aperature with 'bars' across it - take your needle nose pliers and snap off the bars - which should leave you with this:
You can now see inside and see four terminals that come down and four mobile pads that move up to touch the terminals. Get your emery board (I used a small jewellers screwdriver to scrape crap off the pads) and clean up all the pads. Once cleaned, plug only the switch back into it's appropriate connector - set the cars ignition to the run position and check for function. The blower should now work properly in all positions regardless of the fact that the rest of the controls are not plugged in.
At this point you can just reassemble the whole thing if you like, but I started with a little bit of a clean... which could have been a bit of a mistake.
Popped off the sensor duct to find this **** everywhere, 10 years of dead human by the look of it:
Make sure you get well clear of the car before you blow this crap out - there's usually a lot of it in there.
BE WARNED! If you disturb any of the **** off the temperature fan (marked 2 above,) it WILL start squealing annoyingly. Usually just as you've reassembled everything and thinking 'well that was eas... *squeal*' and no ammount of hammering the dash will stop it doing it.