Whos responsibility is blocked drains?

We often get calls from disgruntled people who have blocked drains. A majority of time we can unblock your drains using common methods such as roding or high pressure water. However, a small percentage of the time we find that there is not blockage on the customers property but still they have a foul smell and water is residing in the drain. This is often because the blockage is either further on down the line on a neighbour's property or the actual main sewer line is blocked.

Problems start to arise when the blockage is on the neighbours property but is only causing homes further down the line problems. The argument then becomes 'who is going to pay for the drains to be cleaned'?