Okay, so I've been silly. It's not the first time and it won't be the last. Here's the story so far.
I'm hosting with Hostgator and have an existing site whose URL points into a "home directory" on the server. Great.
I've now developed a WordPress site hosted on Hostgator which I've built in its own folder at http://www.mysite.co.uk/uk. The site URL field has contained this info. The aim has been that when I'm ready to switch to the new WP built site I'll do a redirect in Hostgator's CPanel to point requests for the site to the newly-nominated home directory where the new WP site will be operable. This would then serve the new site.
Trouble is that, like an idiot, I changed the site location in WP-Admin first before performing the redirect.
Now I get a 404 page when calling the WP build! I do get the index.php sitemap but it's naked - no CSS.
How can I rectify this? Does it require a change of data using phpMyAdmin?