Thank you Mike, I spent a long time trying to figure out what was wrong with it, I (foolishly) assumed that there was contact and that it would suffice. Is there an easier way for me to find simple faults like that or is it just experience and common sense? I've extended the relevant faces and it now works.
Regarding the image you attached, is there a way to remove the angled black line from the face or is that there as an indicator for the hidden taper?
The simulation will not allow me to mesh the "combine" that I performed to make it a single part, I am running it on the finest mesh but it still won't accept it, is there something silly I may have missed?
To remove the hidden line, You could just create an extrude through it.
As for the meshing, I would definitely separate the zero thickness geometry, rather than trying to connect it. Finally, on the Tools toolbar, run these two checks. Fixing all of the errors on these tends to make meshes happen. .
With all of that said, take your analysis results with a grain of salt. They will only be valid far from the combines you are doing to get it to run.