I've heard it said that an effective deterrent to this sort of queue-jumping is to break wind loudly and then accuse the queue-jumpers of being the offenders. The richer and fruitier the effusion the better, apparently, aided by dramatic gestures, shrugs, raised eyebrows, grunts and groans. Do it convincingly and you'll soon have the place to yourself. A good Madras or Tandoori the previous day also helps, they say.