To Dave (I'm new and can't send pm yet) and everyone else,

I haven't had time to go and have it scanned for errors. I guess I'm beginning to get used to living with the problem as it only occurs 2-3 times a month and I was given a tip by a mechanic who owned quite a few Audis. He said this is very common with Audi engines and a quick "fix" when the problem occurs is to press gently on the accelerator. I have tested it while static and idling and found that if I press fast and hard I notice a sound just like a swoosh the millisecond before the revs go up whereas if I press slowly it revs up without the odd sound and it keeps the problem at bay. However as I said before the shaking and stalling symptoms are very sporadic so I wouldn't have to do this often. Really weird I know an my feeling is that this is linked to pressure, some sensor misbehaving or air flow...must be something like that.
Nevertheless I aim to have this investigated soon as it has now sparked my curiosity big time.
Once I have news I will update the thread.

PS: I have gone through previous invoices and the car has attended the coil pack recall 2 years ago which kind of rules them out...