Point of order, it's a north west thing - you'll not hear anyone ordering a barm on the right side of the Pennines.
A mate tells a tale of playing a gig somewhere in the wilds of Lancashire (Bacup or Rawtenstall or some other such hell hole) and stopping at a chip shop on the way home for food. The lad in front of him ordered a "chip barm pea wet" which it seems is something of a local delicacy: a chip butty, with the breadcake dipped in the juices of the mushy peas...