What my mother used to use for Sheperd's Pie (She was born and raised in
Dartford, Kent UK)

Was a mixture of Beel, and Pork mostly (like a meatloaf mix), and while
cooking down the Meat, would add a couple of Cubes of Beef Oxo. Oxo does
also come in Lamb Flavor also.

For Steak and Mushroom, or Steak and Kidney Pie, the Beef Oxo Cubes is
still the very best thing to use. There's no comparable substitute.
Mark