I have found the code :
<?php get_the_image( array( 'size' => 'featured', 'width' => 310, 'height'=> 200, 'before' => '<div class="thumb">', 'after' => '</div>' ) ); ?>
in my category.php file.
However, if you look at the page http://miklos.co.uk/category/the-bathonian you will see that the main featured image is out of scale.
I would like to keep the width at 310, and have a cropped/cut height where the featured image is automatically made to 200 height (preferably from centre out, but doesn't really matter).
Any ideas/advice/help would be hugely appreciated.