Duplicate content can really put a dent in your search ranking potential and often a site can have accidental duplication when the site runs on one or more URLS or different versions of the URLS or when the site resolves over HTTP and HTTPS. Fortunately, this is an easy problem to fix in one of many ways.
Checking for HTTP & HTTPS Duplication
First up, visit your site, let’s say it is: http://www.yoursite.co.uk. Now, check if you can also visit the site as https://www.yoursite.co.uk. If the site returns on both addresses you may have some issues which can be easily solved with any of the following options.
1. Stop using HTTPS on pages that you want to index and restrict it just to your transactional pages such as your shopping cart and checkout. You don’t want to index these pages anyway so that provides the best solution. Make sure you 301 the https pages to the http pages to catch any links or bookmarks.
2. Add a canonical link from the HTTPS pages to the http pages
3. Prevent Google and co from indexing the HTTPS pages by adding the meta noindex tag on the HTTPS pages. I would tend to insert this dynamically on all https versions:
<meta name="robots" content="noindex">