Thank you to everyone that has sent our information request to Thames Water. If you haven't, please do!
By sending the email you have your own legal action against Thames Water, for free. Once it has been sent the company has 20 working days to respond.
Hopefully they will recognise that the Environmental Information Regulations oblige them to publish detailed plans for their sewer overflow upgrades on its website and update it when they change. If they don't they are breaking the law. 
The regulations are designed to increase public accountability and strengthen democracy. They are derived from the Aarhus Convention, the UK is a signatory.
The Convention is an elegant expression of why we need citizen activism. It states:
"Adequate protection of the environment is essential to human well-being and the enjoyment of basic human rights, including the right to life itself. 
Improved access to information and public participation in decision-making enhance the quality and the implementation of decisions, contribute to public awareness of
environmental issues, give the public the opportunity to express its concerns
and enable public authorities to take due account of such concerns."
The Environmental Information Regulations aren't just a tool to extract data from a public body. They are a lever to increase accountability and scrutiny. They make the authorities do a better job.
When Thames Water respond we'll email again with the next steps.