My plugs have been changed now, and there's some good news. I think I've found the cause of the misfire problem. The connector (where the leads plug in) on plug 3 was loose, as I picked it up I noticed it spin around. My dad said last night that he's had this causing a misfire on motorbikes in the past. I didn't actually notice this until after having a long drive with the new plugs. I wasn't listening for the misfire, but when I got in I realised that I hadn't heared the misfire, and then I found the loose end on the plug. The car does drive differently too, but I'll come on to that in a moment.
Now, there are two pictures of my plugs on the net. "plugs.JPG", and "plug2.JPG". These can be found at www[DOT]geocities[DOT]com/petermcmillan_uk/. It was very hard to get good pictures because they were so small, it's virtually impossible to even see the carbon arouund the rings. My main concern is plug 2 (which is why there is a seperate pic of it). The thread on plug 2 is the only one with oil on it, and the insulator stuff around the electrode is more golden. Could these be problems? This can just be seen from the pictures. Oh, all of these connectors had black deposits over them, but it didn't cover the whole connector.
When I first started the engine I wasn't expecting any difference until the idle settled down (because that's where the exhausty kinda noise happens). I was wrong though there was a difference almost instantly :o. It wasn't a huge difference, but enough for me to notice it. What happened next really shocked me though. I tried reversing out of my driveway slowly, the back lifted up, and the car shot back. It had clearly effected the performance. For a few roads I also found it harder to keep the speed down. When accelerating fast it didn't feel faster, but I think this was because the car was quieter than usual.
The exhaust still sounds just as loud, but it seems to sound more normal to me. I'll see what it's like for a few weeks, but I think I'm gonna be satisfied with it. Why couldn't the garage have diagnosed this misfire? They said there was nothing wrong and it was normal!