The command works and saves the content to a file as I wanted but wget just doesn't terminate (even when I try this from the command line rather than in a script). I suspect it's the ? and & characters that are causing the problem, if so is it possible to 'escape' these.
Pre-post edit: I just put the url in quotes and it works properly. Doh!
Leaving the post here as it might help someone else who is as thick as me!