Balti wasn't imported ready-made from South Asia — it was invented in Birmingham, and the word just means 'bucket,' describing the pan it's cooked and served in.
Meat, vegetables and spices are cooked fast over high heat in a flat-bottomed, two-handled steel bowl, then brought straight to the table still bubbling, to be scooped up with naan instead of served with rice. Birmingham's Balti Triangle, around Ladypool Road and Stoney Lane, is lined with restaurants doing exactly this.