On 17th December, we noticed that the water was flushing right up to the rim and draining very slowly. The customer care department said "since we had lived in the property for the last 18 months, then the problem could not be with the drains but most likely due to things that shouldn't be flushed down the drains". I was also advised to get a drain blockage company to take care of the problem. I called in a CCTV drain survey company. Two inspection chambers were completely blocked. After hosing with garden hose, they found a contractor's measuring tape in one inspection chamber which was creating a blockage in that particular IC. I did not see any reason why the other inspection chamber was also blocked but had my suspicions. The survey report raised more questions than it answered as I do not know the implications of some of the findings. After jetting, most of the drains had 5% residual water on 100m pipes. Is this normal? Drainage flowing downstream to next door neighbouring property No.11 in diagram below has residual water of 40% of water height on a 100mm pipe. Is this what is called a backfall that is preventing the flow from our property to next door. Attached is a copy of the survey. I think the gradients between IC1, IC2 and IC3 may also be wrong!! Any guidance would be much appreciated!!