In a bowl, whisk together the red wine vinegar, Worcestershire sauce, red pepper flakes, shallot, garlic, pepper and salt. Whisk in the olive oil. Trim as much remaining fat as possible from lamb and in a shallow dish spread oil mixture over both sides of it.

Prepare grill or heat grill pan over medium heat. Bring lamb to room temperature and grill on an oiled rack set 5 to 6 inches over glowing coals 10 to 12 minutes on each side, or until meat thermometer registers 140 degrees, for medium rare meat. Alternatively, lamb can be grilled on a grill pan for about the same amount of time per side. Transfer lamb to a cutting board and let stand 10 minutes. Serve lamb thinly sliced across the grain, with relish.