Thought I'd break my silence with some useful information I've just found...
Despite my local Audi dealer adopting the seemingly now widespread "we don't give out part numbers" approach, I've managed to combine their answers with some of my own research - mainly from this thread - and experience.
Our little A2 has a the ABS warning lamp on and has subsequently failed her MOT. The code readings were as follows:
606 YAW RATE SENSOR
01117 RHF SPEED SENSOR
046A ABS MODE SIGNAL
0606 YAW RATE SIGNAL
So I've dispatched her to a local garage to get the ABS sensor and/or bearing changed as I don't have the time at the moment. I also ordered, on the strength of the posts above, what I believe to be a combination sensor - part number 7E0907655A - and, well, still no joy. The new unit is much larger than the original, has a four-pin connection when the original is expecting three and the plug position is such that the original wire won't really fit without excessive pulling. Fitting the new sensor has not cleared the 606 fault code.
The story is a bit ongoing, as I've not had a resolution yet - but the interesting thing I found is that Audi do still stock the separate yaw rate sensors and they're currently in stock at their warehouse. They've got a hefty £560-odd price tag, but that's not my point - what I'm saying is that newer combination sensors
do not seem to work on the earlier vehicles, if this happens to you it seems the solution is to replace the
original yaw sensor with another single item.
Will update when I've got a resolution, if anyone's still speaking to me