£3.6bn tunnel is proposed to stop sewage being dumped in Windermere, but the Government must still back it

Raw sewage and treated effluent still pour into England's largest lake, and campaigners blame them for turning parts of Windermere green each summer. United Utilities wants a 12-mile tunnel to carry the waste away. Up to 86 miles of new sewers would connect 12,800 people to the network for the first time. Chief executive Louise Beardmore calls it a '100 year solution'.

Activist Matt Staniek warned: 'For me this is a plan on a piece of paper.'

Backers claim £7.5bn of benefits, against £2.5bn otherwise spent on piecemeal fixes.

The lake holds 300bn litres, and water takes nine months to cross it.