This song doesn't seem to be in the Digitrad. The song is about a band on the last night of a booking at a pub. After hours, the band is having a last drink and jamming with wht pub owners when the door opens and two constables walk in

         "......mean and slow
         "Saying, 'Play the Mason's Apron,
         "It's the only song we know.'"

Can some one tell me the rest of the words? And who wrote it?