Rishi Sunak will lose “dozens of seats” at the next general election if he fails to stop sewage being pumped into rivers, according to Sir Ed Davey.

The Liberal Democrat leader pressed for greater action on “one of the biggest environmental crimes in our country” as he spoke at his party’s spring conference in York.

Water companies are only permitted to release sewage during periods of heavy rain so the system does not back up and pump sewage into people’s homes.

But campaigners last year warned firms released raw sewage into UK rivers and seas almost 150 times during dry weather in a 12-month period.

The issue has become a key battleground for the Lib Dems in Parliament as they bid for swifter progress to prevent sewage dumping.

Sir Ed stressed the need for “empowering people” to be part of decisions for their community, adding in a message to Tory MPs: “People want good schools, good hospitals, affordable housing and safe communities.

“People want a clean, healthy natural environment. They want an end to the Conservatives letting water companies get away with pumping filthy sewage straight into our rivers.

“That is one of the biggest environmental crimes in our country today and it’s a crime that will cost the Conservatives dozens of seats if they don’t act.”

Take economic growth. Remember when governments used to talk about targeting three, four, five per cent? Rishi Sunak’s target - anything above zero. It’s like a mid-table football club with a new manager, targeting to avoid relegation rather than a place in the Champions League

Government plans released last month outlined how water companies in England will be required to explain why sewage spillages into rivers and seas are happening and what is being done to fix them.

Ministers are also consulting on making it easier and quicker to slap polluting companies with penalties, so they are made to pay immediately rather than wait for lengthy criminal prosecutions to conclude.

Sir Ed earlier criticised Prime Minister Mr Sunak’s “total lack of ambition” to solve people’s problems and said the Government must be “put out of its misery”.

He compared Tory MPs to “mutinous pirates” as Britain encountered choppy waters, telling Lib Dem members: “We needed Hornblower. They gave us Pugwash.”

Sir Ed added: “Take economic growth. Remember when governments used to talk about targeting three, four, five per cent? Rishi Sunak’s target – anything above zero.

“It’s like a mid-table football club with a new manager, targeting to avoid relegation rather than a place in the Champions League.

“Jeremy Hunt in his Budget on Wednesday, proudly boasting not that the economy is growing, but that it might just avoid a technical recession after all. Total defeatism from a Government that’s run out of ideas and has nothing left to offer.

“The way Conservative MPs talk nowadays, it’s like they know the truth: their Government needs to be put out of its misery.”

Sir Ed said Labour’s ambitions are “hardly much higher”, noting: “Their only goal seems to be: ‘Not as bad as the Conservatives.’ Talk about a low bar.”

The party leader received sustained applause from members as he spoke of the need to “repair our broken relationship with Europe”.

He claimed the Lib Dems have a “real plan to fix Britain’s trade”, which will “tear down the Conservatives’ trade barriers, rip up their red tape, and rebuild the ties of trust and friendship with our European neighbours”.

Conservative Party chairman Greg Hands dismissed the attack on his party by Sir Ed, saying: “Time and time again, the Liberal Democrats have shown they cannot be trusted to deliver for the British people.

“They are out of touch with the people’s priorities on key issues like housing, energy and immigration.”