sewerage

Professor William Alexander Donald said they resembled fat, oil, and grease blobs - often called fatbergs - which are commonly formed in sewerage systems.

Water UK, the industry body for sewerage companies, said this was "unacceptable", but argued that the record levels were due to heavy rain and increased data collection.

Most of the UK has a combined sewerage system, meaning that both rainwater and wastewater - from toilets, bathrooms and kitchens - are carried in the same pipes.

Based on an average annual water and sewerage bill of £440, this would be around 10% of the average annual customer bill, with several higher payments worth at least a quarter.

Some payments could amount to customers claiming at least a quarter of their annual water and sewerage bill.