If anybody is interested - I've got the mobile page score up to mid 50s. My OCD is calming...
I also added
<link rel='preload' href="https://bsparkle.co.uk/themes/niara/fonts/font-awesome/fontawesome-webfont.woff2?v=4.6.3" as="font" type="font/woff" crossorigin>
in the header.tpl - I doubt it made a significant difference but Google liked it.
I also changed the social widgets around and turned some off on mobile.