Engine light on, misfire, knocking

Just took my 8 up to the shops, noticed a misfire via putting it in drive and it not being a smooth "bite" - more of a jerking movement. Got to shop (2 miles), noticed it again when reversing. Drove back to work, idling down the car park with the window open, there's a light knocking sound and now the engine light's come on.

I pipped the bonnet and had a listen, I can feel the knock on the top of the engine, the right side near the oil filler, but it doesn't get louder when I take the filler cap off. Sounds like someone tapping a margerine tub. I'm gonna get someone to give me a lift home to pick up my laptop and use vagcom for the first time.

Questions:- what would it sound like if it was a simple misfire (electrical/fuel)?
Anybody know what it would sound like if there was a sticky valve?

More importantly, does anyone know what this is likely to be or have you heard a noise like it? Does it come across as serious? I'm panicking now as I have to tow my caravan 25 miles up the road this weekend.

2002 S8. Any help/insight/advice appreciated - I'll also update in a bit with the vagcom results...