Retired detective Ash Smith, played by David Thewlis in Channel’s 4’s shocking new docudrama Dirty Business, talks about his decade‑long investigation with neighbour Professor Peter Hammond into England's water companies and the incredible response to the programme. It’s a dramatisation of the real-life story of how they uncovered the illegal dumping of raw sewage by water companies in Britain’s waterways and it's drawn a huge response from the public.  Ash explains how they started to put the pieces together; used sophisticated machine learning to interpret complex data; challenged water companies and the Government’s Environment Agency with compelling proof; and ended up giving evidence in Parliament. Ash co-founded Windrush Against Sewage Pollution.    Professor of Computational Biology Peter Hammond - co-founder of WASP - with Ash Smith WASP's Ash Smith and Peter Hammond with their acting counterparts David Thewlis and Jason Atkins David Thewlis in C4's Dirty Business