www not resolving domain mapping

Is someone able to help me resolve this issue.

http://andrewclarkson.co.uk - returns site
http://www.andrewclarkson.co.uk - 404 error but should return the site.

Here is the contents of my htaccess file:
AddType x-mapp-php5 .php

php_value upload_max_filesize 20M
php_value post_max_size 20M
php_value max_execution_time 200
php_value max_input_time 200

RewriteEngine On
RewriteBase /
RewriteRule ^~(.*)/(.*).html$ a2pLink.php?postID=$2

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# uploaded files
RewriteRule ^files/(.+) wp-includes/ms-files.php?file=$1 [L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule . index.php [L]