Keeping his claims small, around £3k, at around a level we presume at which the computer could dispense money without human intervention, he made a total of 218 claims for fictitious people, the proceeds of which were paid into 74 different bank accounts. He netted £559,497.42 before he was caught.
Since I've heard of this fraud from a few other sources, I'll bet it's widespread. Not to the extent of 218 false people, but maybe one or two, each netting a couple of grand or so. The less greedy the fraudsters, the longer they can get away with it.
For both taxes and benefits, the lesson to be learned is that the more local they are, the less likely they are to be subject to error or fraud.