Had a quick look at this (although there is no coil installed currently) but it's bleddy tight and when I did manage to screw it one way or the other the top piece with the positive post and airhole rotated round. Does that top bit unscrew and if so should I remove that before I do this?
Yes it does unscrew adam, but you don`t need to do so with it. As i said i have had to loosen a couple of mine, and the block is a tad loose, but at least they fire up. It is the screw which needs to make contact with the 510 connection on your mod if that makes sense.

typical ...looks nice! Do you get extra flavour?
don't think I got extra flavour with the last bottle, but I have just ordered some more MBV juices as my first batch is getting low, including 15ml of Blue Moo that you are all raving about +1 on that and the Bavarian Cream and +2 on the Caramel Coffee, Dulce de Leche & Graham Cracker and Morning Vape
I'm fine thanks, so no need to worry.