this is true - had ours unblocked last month. Every house attached to
that sewer until the point it meets the main sewer (water company
owned) is legallaly obliged to contribute to teh unblocking costs.
It'll tell you this on any water company's website. The dynorod guy
even wrote "this bill must be shared" on the report he wrote out.
Dynorod was £120 but he unblocked 2 drains. Expect about £80