Unfortunately, Cannondale no longer offer a frame exchange program in the UK. This stems from the fact that they no longer retail frames at all in the UK market (other than the Supersix EVO), and therefore don’t have the stock to draw from for frame exchanges.
This is according to an email I received from them after I enquired myself. According to the same email, the website is maintained by Cannondale USA and as a result they have simply copied and pasted the FAQ page onto the UK site without modification. They are now working to have the frame exchange section removed.
It’s a shame, for sure, but if your bike is in good nick, Ebay or a part-ex at your dealer may be the only way forward.