Samples taken by the Save Windermere campaign last month at Ambleside showed cyanobacteria concentrations above WHO guidance for recreational use of the lake

A 100-metre-wide algal bloom left an area of Windermere unfit for bathing, tests have revealed, as campaigners blamed United Utilities for continually dumping sewage.

All 11 water and wastewater companies in England and Wales are now under scrutiny over sewage spills, after the regulator said it was expanding its investigation.