Britain's highest water bills are set to be cut by £50 a year as MPs voted through a £400 million handout to a private company.
South West Water customers, mainly in Devon and Cornwall, pay more than consumers elsewhere in the UK but the Commons has agreed to reduce their bills through the Water Industry (Financial Assistance) Bill which is being rushed through Parliament.
The Bill was given an unopposed third reading and the Government has asked Commons Speaker John Bercow to certify the legislation as a money Bill, meaning the House of Lords cannot amend it and guarantees it a swift passage to the statute book.
Environment minister Richard Benyon said: "We wanted to get on with funding South West Water to enable it to cut bills for its household customers."
The legislation also means the Government will be able to limit the cost to London residents of building a Thames Tunnel super-sewer to carry waste water.
Household bills were tipped to rise steeply because customers funded the much-needed infrastructure project but the state can now give financial support to the Thames Water firm to keep down costs to customers.
"We want to reassure potential investors in the Thames Tunnel from an early stage that the Government is willing to provide contingent financial support for exceptional project risk where this offers best value for money for Thames Water customers and taxpayers," Mr Benyon said.
He claimed the scheme will directly create 4,200 jobs, with thousands more in supply chains.
Shadow environment secretary Mary Creagh said the Bill "corrected a historic injustice" for water customers in the South West and "lays down powers to provide finance for infrastructure investment".
Liberal Democrat MP Dan Rogerson said customers in his North Cornwall constituency fund the cleaning of the region's beaches through higher bills and welcomed the new cash to reduce their household spending.