Well, she towed just fine, no problems at all. Managed to get my van (which weighs about the same as the unladen car when loaded) towed off the muddy field it was in and on to my usual pitch closer to work.

Incidentally, I was impressed that Autopool were a bit vague with the fault diagnosis until I held the phone near to the source of the knocking sound, and straight away he said "Turn her off, don't start her up again, don't drive her or you'll break something - it sounds like a spark plug's gone through the hole, get it transported down here and we'll confirm it". Sure enough, that's exactly what it was, as I confirmed myself. Either phone quality has moved on a lot or that guy knows these engines very well!!

I didn't get much chance to have the craic with the guys as I got a lift off someone from work who I had to guide there, he wanted to get back promptly, but from what I could gather it was a bit tricky for them to do the helicoil in situ as the spark plug recess is so deep, but it went fine. The shavings were blown out of the cylinder afterwards with compressed air. I'm not entirely sure if this got ALL the shavings out (I hope so), but they seemed happy enough that it was a successful operation and the engine runs slightly smoother now (it's cured my slightly wavering tickover too).

He checked all the other plugs, found no.3 was loose, so that's been tightened up too.

I think the moral of this tale is 2-fold, firstly, change your own spark plugs then you know it's been done properly, if possible try and use a rag & some cleaner on the threads a little before screwing the new plug in to specified torque. Secondly, if you develop any sort of misfire (audible or via vag-com) or wavering tickover, or there's a juddering when in drive and braked stationary, get in there and make sure all the spark plugs are tightened down to the specified torque.

I think I'll be tempted to use something on the threads when I do the plugs, like copper grease or a dab of engine oil, as he commented that it can just as easily be the other way, where the spark plug is seized into it's recess (there was a dark green/blue A8 on an "N" plate with this problem).

Any thoughts on this? Perhaps thread seal, as it's supposed to lubricate on loosening as well as grip when tightening apparently?