Original post was by Craig Childs, many thanks to him. And just in case the link will expire, the solution is as below:
What was happening was when the Write>Post screen was opened, it would sit then eventually throw up an unresponsive script error which stemmed from: /wp-includes/js/jquery/jquery.js
It essentially rendered the Wordpress admin useless unless you wrote a draft elsewhere, such as an external blog editor, and saved it as a draft - the Manage section was unaffected.
In any case, if you find yourself with the same issue, it's a simple edit of the wp-admin\edit-form-advanced.php file. Just remove this line:
$metadata = has_meta($post->ID);