OK, so Chris has had the A8 up on the ramps and stands this evening. The oil level is good, it is full, but the colour of the oil was not the yellowish-green colour we were expecting.
Gearbox oil level & type check 011 by
SnrSarg, on Flickr
As per the invoice, there is no evidence of new filter, so they have only changed the oil, nothing else.
The car has only done 150 miles maximum since the oil change, but definitely does not look like oil that new as there seems to be too much debris/sediment in the oil, although that could have come from the filler plug.
Any suggestions for the next step?