Funnily enough I got mine back from the dealer last week after fixing this exact fault. Symptoms were that either the cc wouldn't come on at all or would work for 5-10 minutes then switch itself off, not resetting until after you'd switched the ignition off and restarted the engine.
Dealer said that the switch on the stalk was at fault and this has been replaced. All is now well.
Looks like you need to get down to the dealer.
Simon