Thanks Katie, I'll give the upstrokes a go with a pencil as practise. I do hold the pen fairly light though, in fact on some of the upstrokes I am literally using the weight of the pen to draw, but it's still scratchy.
Erica - I bought myself the Speedball Set, and it came with a bunch of nibs, for both pointed pen and broadstroke/blackletter writing. I think the ink that came with it is fairly cheap as well, as I am prepping the nibs by following Schin's excellent advice. I also clean it regularly whilst writing, so I think it's a combination of cheap ink and cheap nibs!
I bought some Rhodia R paper, and I will get myself a few different nibs, and possibly some decent Sumi ink after Xmas. The plastic holder doesn't allow me to adjust the angle of the nib on the paper, plus when the nib is in, it is not in the centre of the pen holder either. Any recommendations for nibs? I like the look of Hiro 41's, and some of the Brause ones look nice too.
Also, I noticed in your tutorial videos that you're not writing in line with the slant lines. Someone told me to keep the tines of the nib in line with the Copperplate slant, but I really struggle with this. My pen angle is more like yours in the videos, which I find much more comfortable.
Thanks for all the advice so far!