Hi and welcome to the forum !!!
This is a common problem on the 1.8T which is caused by oil sludge ...
If you have a read of A8 tech guide on this it will show you whats needed to be done to rectify the matter, but Audi are right in a way you shouldnt really drive it too much with the problem as you can restrict the flow to your oil pump and then you could be looking at big trouble with engine damage occurring !!!
If you want to save a few quid you should be able to get an independant garage to clean out the oil strainer(gauze) and hopefully you should be all okagain ...
http://www.audi-forums.com/b6-forum/...ure-light.html