Thanks to Ian's help (who was spot on with the diagnosis!), I have now resolved this little problem. As there were some slight differences to the illustrations shown in the Audipages article, I will add my own short 'how to' here...
1. No prizes for guessing that this is how it looks before anything is removed
The 2 screws securing the airbag to the wheel are located behind the wheel and can be clearly seen in the next photo.
On my wheel, they are Torx T27 but on others apparently T30.
2. Here you can see the 2 screws protruding from the rear of the wheel (they are held in place by a washer once the airbag is removed, so you don't need to worry about them dropping out).
The airbag is connected to the wheel in 3 locations (in the multifunction/tiptronic version). Only 1 is shown in this photo.
You can also see the cable which connects the slipring to the wheel here. This needs to be disconnected from the wheel before removal.
The large nut that you can see in the centre secures the wheel to the steering column. This is removed using a 12mm splined socket. A T55 Torx apparently does the same job.
3. Wheel now removed and slip ring visible. In order to see the 'window', the top column cover has to be removed. This is secured by 2 screws located on either underside of the column as shown in the next photo.
4. A small phillips screwdriver removes these (at least on my model).
5. Here you can see the gold colour in the window - this is the correct, 0degree, position of the slip ring.
For those of you who have read the Audipages article, the first thing you will notice is that there is no 2o'clock position marker on the slip ring. Instead, there is an 11o'clock marker, which has unfortunately been obliterated by the flash although it is partly visible in photo 6 (a bizarre design as the 2o'clock marker makes so much more sense as you actually have something to line it up with, ie the window!
6. Here, the window has changed to what I would call 'half-gold' - this is the 360degree position (a full turn to the right).
7. Here, the window has changed to black - this is the 720degree position (a further full turn to the right).
As we all know from the best written manuals, reinstallation is the reverse of removal, but here are the key points :
With the slipring in the correct (gold window) position and centred (using either the 11o'clock or 2o'clock markers), refit the column cover and then centre the wheel on the spline and secure with the nut until tight and with the markers on the nut lined up as shown in photo 2.
Reconnect the slipring cable and the airbag connectors to the wheel before resecuring the airbag with the 2 Torx screws from behind the wheel.
The ESP and ABS warning lights in the dash should now go out when you restart the engine. If they don't then either :-
- the slipring is not in the gold 0degree position;
- the steering angle sensor (G85) needs recalibrating using Vagcom (VCDS) following the procedure here
http://www.ross-tech.com/vag-com/car...ringangle.html ; or
- the sensor is broken
If the airbag light comes on then you need to clear it using Vagcom. If it still remains on, then you have a loose connection or other electrical fault.
Hope this helps anyone encountering a similar problem.