Is there a dual licence (Mac/Windws) option and are they interoperable?
Here is the relevant article on the topic of licensing, and here is another regarding cross-platform compatibility. Short answer is “No” and “Yes”, respectively. 
Ok, so how about me using a single windows licence on my desktop and laptop?
Is that permissable?
Thanks
Ah ok, the knowledge base seems to supply the general answer, so it looks like I can install the software on my desktop and laptop, but rather than keep transferring files from one machine to another it would probably make more sense to use the laptop as the ‘master’ (powered on) and use a windows share for the desktop to access the laptop.
That way I could pick up the laptop anytime and have the latest files available.
Maybe there’s a quicker way of just syncing permanently using my linux server. Perhaps a git repository on the linux box might work better.
Git works pretty well in my experience, but really any method you would use to copy files and folders between machines is applicable. Thumb drives, FTP, Dropbox, whatever… it all works well. Obviously with some of the techniques you need to be a little more careful. For instance if you are sharing your files over LAN, you want to make sure only one computer has the project open at once. Likewise with Dropbox, but additionally because it requires transmission over the Internet, you also have to be careful of transmission latency. It may take a few seconds or minutes to fully acquire the latest copy of the project, and opening it prematurely could cause mild conflict-based corruption.