Thanks for that Marcus, I'll have to look into getting the most up to date version (though I'm not getting a plugin update notification on my dashboard).
I had to take a slightly different approach, as my social media bar is in my header.php file and shared across the entire site.
I'm NOT a php developer so please don't mock me if this is totally the wrong solution - am always grateful for advice from those with greater programming skills :)
echo esc_url("http://www.supporthandmade.co.uk" . ( $_SERVER['REQUEST_URI'] ));
The reason I did this was that if I didn't explicity put my domain at the front, I only got the 'slug'. It does seem to work for all pages. What I don't (yet) understand is if this is making extra calls to the server or extracting the information from elsewhere (sorry, I'm hopeless!)
I'm beginning to think it's my template that's at fault, as it's doing wierd things with my meta data too :-/ Sadly I'm so far down the design road now that I simply can't afford to find a better template without switching the site off for a few weeks. In any case, having to fix things like this myself is helping me learn PHP.