I just had a windscreen chip repaired by Auto Glass, who did a good job. Due to the damage only having occurred a few days ago, the repair is almost invisible. The operative gave a good tip, which I think is worth passing on. He said that if sellotape is put over the chip until a repair can be made, it keeps out dirt and water from between the laminated layers - which enables a better end result and reduces the chances of cracking due to water freezing between the layers.