Sgt_Kickaxe - 9:04 am on Jun 23, 2012 (gmt 0)
including new layout, CMS, urls and meta title structure...
You have all new urls? Forget what's on the pages, if the urls have changed at all, even one character, then your pages are all considered new and their content duplicate(because Google knows they've seen that content on your old urls). The new urls won't rank as well and the old will fall out of serps since they are no longer there.
All incoming links to your old urls are also pointing to the wrong pages.
You can make sure that you add 301 redirects from the old urls to the new urls that have the exact same content. Even if you do this you can expect a loss in traffic as 301's don't carry the full value, some is lost.
Moral: never, never, never, never, never change the urls unless you have no choice(new CMS,removal of parameters due to poor rankings, etc).