I agree with Andy, www - non www doesn't matter. I would go with a redirect to the non www since most of your links don't include it. I also recommend along with the 301 redirect utilizing the canonical tag and setting the preferences in Google webmaster tools.(what we do). If your using a Linux based server here is the .htaccess code to redirect to the non www (be sure to place it at the top of the .htaccess)
RewriteEngine On
RewriteCond %{HTTP_HOST} !^yoursite.co.uk$
RewriteRule (.*) http://yoursite.co.uk/$1 [R=301,L]
(you may already have done this since you mentioned that the site currently resolves to the non www version, but I included it for anyone who may be considering it).If it's not feasible to utilize the .htaccess still use the webmaster tools and canonical options at the very least:
As for the drop in rankings I personally noticed a few of my stores dropped in page rank recently around the same time Google released it's Panda updates. These stores were placed into a link building software that a company I used to work for created. I suspect that since a good chunk of these links were distributed onto blogs that were spam in nature, this may be the cause of the drop, but it's not for certain. So if you participated in some gray or black link building in the past with your site then this could be the reason as mentioned in this article [As for the drop in rankings I personally noticed a few of my stores dropped in page rank recently around the same time Google released it's Panda updates. These stores were placed into a link building software that a company I used to work for created. I suspect that since a good chunk of these links were distributed onto blogs that were spam in nature, this may be the cause of the drop, but it's not certain. So if you participated in some gray or black link building in the past with your site then this could be the reason as mentioned in this article http://searchenginewatch.com/article/2067687/Google-Panda-Update-Say-Goodbye-to-Low-Quality-Link-Building Best of luck!">http://searchenginewatch.com/article/2067687/Google-Panda-Update-Say-Goodbye-to-Low-Quality-Link-Building](I agree with Andy, www - non www doesn't matter. I would go with a redirect to the non www since most of your links don't include it. I also recommend along with the 301 redirect utilizing the canonical tag and setting the preferences in google webmaster tools.(what we do). If your using a Linux based server here is the .htaccess code to redirect to the non www (be sure to place it at the top of the .htaccess) RewriteEngine On RewriteCond %{HTTP_HOST} !^yoursite.co.uk$ RewriteRule (.*) http://yoursite.co.uk/$1 [R=301,L] (you may already have done this since you mentioned that the site currently resolves to the non www version, but I included it for anyone who may be considering it).If it's not feasible to utilize the .htaccess still use the webmaster tools and canonical options at the very least: <link rel= "Search Engine Watch Panda Update")
Best of luck!