Cambridge publishes that it doesn't accept non-radio traffic. However there is a local rule (I'm told, but haven't seen written down anywhere) that a based aircraft returning from a local flight with a radio failure can just follow normal radio failure procedures, ie 7600 if possible, fly along runway at 600' waggling wings and looking at the tower for a light. (If I remember that correctly from decades ago.)
A controller once told me that he did actually know which cupboard to look in for the lights.