In my experience giving problems like this to a workshop to diagnose, ends up resulting in lots of money being spent, and often parts being replaced that don't need to be.... so, I hope to diagnose this problem based on what info I find out here. I believe People should learn how to fix problems on their own, without always having to run to a workshop all the time. Workshop is a last resort. Sorry to rant, but if I wanted to get a workshop to diagnose the problem, I wouldn't be asking for the advice of people on this site....

Cheers Tuna, will check the plugs and report back...