Experts believe the sinkhole, which has left 50 homes without power, was caused by the collapse of a unrecorded mine. Five homes were evacuated in the early hours of Thursday after residents heard a crash and the hole appeared. A small hole in the footpath was cordoned off last week, but Hertfordshire County Council said there was "no reason to suspect that the hole would collapse". One local resident told the BBC his wife had previously seen a postman fall in the smaller hole and he had looked "quite badly injured". (BBC)