Cruise Control

I have a problem with the cruise control being intermittent. My question is wether it is likely to be the vaccum system or the stalk. The symptoms are that it either works or doesn't, and turning the car off and on can change this, but sometimes while it is on for any number of minutes it will suddenly cut out and not come back on again until the engine is turned off and on again but this doesn't alwaye cure it.

Thanks