Today i spent some time playing around with the tension on my sewing machine. After a bit googling, I found this site: http://www.treadleon.net/sewingmachineshop/tensionadjustment/tensionadjustment.html
I followed it right through, thought it wouldn't hurt given my machine is older and I don't know it's service history. I have wondered in the past whether the top tension adjustor-thingy actually worked. Now I know it does, so that is handy :) I also adjusted the bobbin tension and I can now get a lovely even stitch. Woo Hoo! This should make my sewing a lot less stressful. If you're at all curious about tension, give the link a read, it's written by a machine servicer, but it is easy to read and indeed, quite humorous.
I'll see how the machine runs over the coming week or so and rethink whether it needs a service. Hopefully I've saved myself a hundred bucks!