Solved! For anyone interested, I missed a line of code (RewriteBase /) out.
Heres what I eventually used:
Code:
Options +FollowSymLinks
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^script\.example\.com
RewriteRule .* - [L]
RewriteCond %{HTTP_HOST} !^(.*)\.example\.com/uk/$ [NC]
RewriteRule ^(.*)$ http://www.example.com/uk/$1 [R=301,L]
Thanks!