we are having an extension built and a fork lift truck driver had no choice but to access our property by first going on our neighbours driveway. whilst doing this his back wheel caught their manhole cover (which was loose/slightly damaged to begin with) and it lifted slightly. when the neighbour reversed out of the driveway a few hours later, the manhole cover fell down the manhole and left a big hole at the top of the drive with about a 20ft drop. our neighbour and ourselves are now blaming the fork lift truck driver but they are not accepting responsibility as they said the cover was loose before they went on it and can see by google earth images that it wasn't in perfect condtion. who is liable for this?