Firstly let me apologise for not posting more often!
Secondly, Google has specified a way in their Official Google Webmaster Central Blog for you to “Specify your canonical”, or in layman’s terms, say which of your duplicate content pages on your site is the original.
Whilst it’s not a problem for any of the sites I look after or run (I think it’s so much easier just to avoid the whole duplicate content minefield, and why would you want the same content on several pages of your site anyway?) at least I can tell you all that there is a way to fix it.
Add the following code to all the pages the duplicate content appears on, changing the URL to your preferred version of the content: <link rel=”canonical” href=”http://www.example.com/product.php?item=swedish-fish”>
This tells Googlebot that although a page may have the same content as another page, Googlebot knows which is the “proper” version of the page.
But as I said earlier, surely it’s easier to just avoid the whole situation in the first place.