Ok, first of all, I've searched through many threads!
How do you remove the centre section of the start button? I understand the NA is glued on, I've tried gently prising the button off but it seems quite secure but I don't want to force it (what with it being my own car and all
). I don't want to remove and replace the whole switch, just the button, can it be done without removing the dash? 
Hi,
No, the NA isn't glued on. The body of the switch comes away from the front button bit. It's held in place by a plastic push-in nib. I bet the Turbo one is the same...
The button assembly has two long plastic tangs that protrude fron the back of the button. The switch body slides over these two tangs, and has a little plastic retaining nib holding the switch body onto the tangs.
Remove the dash, and look at the back of the switch - it has three push-on metal connectors on the back. Alongside these three connectors you'll see two square holes in the plastic - inside these two square holes is the ends of the two tangs that come from the front "button" part. The tang with the retaining nib is on, is the one that forms part of the edge of the switch-body. Push this edge-bit of the tang in and the body of the switch should come off.
If I could post pictures I'd add one, but I can't do it now - stupid idea to remove this facility. If you send me your email I send you the pictures.
Ah, you mean the "pushy" bit - the actual button. That's a different matter - don't know!
Steve