A petition will be handed in to Downing Street today against the planned Hinkley Point power station as speculation continued that the Government was set to give the project the go-ahead.
The 300,000 name petition follows an opinion poll commissioned by Greenpeace which showed that public support for the £18 billion scheme had fallen to a new low of only 25%, whilst nearly half opposed it.
The petition calls on Prime Minister Theresa May to drop Hinkley and invest in renewable power instead.
John Sauven, Greenpeace executive director, said: "Support for Hinkley is at rock bottom.
"The public knows what the Government has yet to learn - investment in renewables should be prioritised over nuclear power.
"The Government shouldn't risk taxpayers' money on old-fashioned, flawed technology. It should be investing in the future."
French energy giant EDF has already made its final investment decision on the scheme, but the Prime Minister stunned the industry by saying she wanted to review the details.
An announcement has been expected since the start of the week, but could now be made just before the Commons recess ahead of the political party conference season.
During her recent visit to the G20 summit in China, Theresa May defended the delay, insisting it was down to "the way I operate" because she wanted a fresh look at the evidence.
The go ahead will spark a fresh row about the high cost of energy from Hinkley, with EDF being paid £92.50 per megawatt hour of electricity generated.
A Chinese firm has a third stake in the scheme and is hoping to build other new nuclear power stations in the UK at Bradwell in Essex and Sizewell in Suffolk.
Justin Bowden, national officer of the GMB union, said: "Giving the thumbs up to Hinkley is vital to fill the growing hole in the UK's energy supply needs.
"It will be a big relief for the 25,000 quality jobs which were put at risk by the latest delay, never mind the reputational damage inflicted on UK plc.
"The GMB has always had reservations about linking Bradwell and Sizewell with the contract for Hinkley.
"The Government should never have allowed the country to be held over a Chinese barrel."
Juliet Davenport, chief executive of independent renewable energy supplier Good Energy, said: "The decision to go ahead with Hinkley C is a bad move.
"It will take at least a decade to build and leave our grandchildren an inheritance of high energy costs, hazardous waste, security worries, and a plant that needs complex and costly decommissioning."
Stop Hinkley spokeswoman Sue Aubrey said: "There is no widespread support for new nuclear, particularly at Hinkley Point.
"Consumers can tell that the project may be unconstructable, requires vast subsidies and would generate electricity too expensive to use."
The Prime Minister's official spokeswoman stressed that the deadline for a decision on Hinkley Point remained the end of September.
She said: "We made very clear when we set out the timetable in July that it would be by the end of September. We did that knowing the parliamentary timetable."
Asked whether the decision had to be announced in the Commons, the spokeswoman said only that ministers would "keep Parliament updated on the decision moving forward", adding: "There is no update on this. We have set out very clearly what is going on.
"We are committed to making a decision by the end of the month. That's the approach.
"We haven't taken the decision yet. The Prime Minister has not been in touch with the Chinese."
Kate Hudson, CND general secretary, said: "We urge Theresa May to put the interests of the country first when she makes the Hinkley decision.
"The basic facts have not changed: the nuclear power deal is hugely expensive - a £30 billion subsidy will be handed to the French state in addition to what consumers pay.
"It's dangerous: cancer clusters, nuclear accidents and disasters like Fukushima, and there is still no safe way to store nuclear waste."