WHAT caused a landslip hole to appear at the top of an unstable road in Lyme Regis remained unclear yesterday. South West Water told the News it had completed a CCTV survey of its sewers beneath Cobb Road - which is due to be stabilised with a £2m protec tion scheme next year - and had not found any leaks. It had been thought that the slip, which happened last Wednesday, was caused by afractured sewer pipe and South West Water engineers had been investigating the problem ever since. Dorset County Council was topping up the subsiding road until South West Water could plug the leak, but yesterday the water company said it was not respon sible for the landslip. Dorset County Council engineer Kevin Chileda said they now thought the leak could be coming from a private lateral connection - a sewer pipe coming from a nearby home or commercial property. He said: "We've managed to eliminate the main sewer but obviously the prob lem is still there." He said county council engineers were now working with the district council to solve the mystery. He said: "We think they might be able to help us. They own the Holmbush car park and might know where some of the other laterals will come in to the main sewer." Mr Chileda said the problem could also be ground water coming from leaking drains or a new spring. He said ideally they would dig up the road to find the problem but because it was such a narrow part of Cobb Road, it would mean closing the road. He said county council engineers were monitoring the subsidence and topping it up every other day until they could solve the problem.