An MP said Thames Water’s new business plan which would see a 44 per cent surge in bills "is throwing more money down the drain".

Britain's biggest water firm, which has 16 million customers in the Thames Valley and London, has put forward new plans to boost spending and investment in its network by another £3.1 billion.

If regulator Ofwat was to give the full plans the go-ahead customer bills could rise by another £19 to £627 by 2030.

Liberal Democrat MP for Oxford West and Abingdon Layla Moran said: “All Thames Water are doing is throwing more money down the drain.

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"Ministers must ensure that the people of Oxfordshire have a water company able to keep the taps running.

"It would be an absolute disgrace if customers are forced to foot the bill for Thames Water's shambolic failings.

"Ofwat cannot allow these bill hikes to go ahead.

“Thames Water have resolutely failed the people of Oxfordshire with hundreds of thousands of hours of sewage spilling into our the rivers, blocked drains causing effluent overflows, and millions of litres of water lost to leaky pipes.

“The Liberal Democrats tabled a bill in parliament on Monday (April 22), which would immediately put Thames Water into special administration. 

“This is the only way Thames Water can become a financially safe company which cares about the environment.”

Thames Water chief executive Chris Weston said: “Our business plan focuses on our customers’ priorities.

“As part of the usual ongoing discussions relating to (the business plan), we’ve now updated it to deliver more projects that will benefit the environment.”

A Defra spokesman said: “Customers cannot be expected to pay the price for Thames Water’s poor performance, which is why Ofwat should use their full powers to protect customers and ensure value for money in their bills.

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“As with all water company plans, this is not yet final and Ofwat will now independently scrutinise this latest version to ensure it delivers for customers and meets the company’s legal requirements and government targets.”

Mike Keil, chief executive of the Consumer Council for Water (CCW), said: “We should not lose sight of the fact that only 16 per cent of its customers thought the company’s proposed bill rises in its five-year plan were affordable.”

Gary Carter, national officer of the GMB trade union, called on the firm’s shareholders to “fork out to give the company a chance to turn things round”.

Ofwat is due to give its initial decision on the proposed business plan, known as PR24, on June 12.