Tony Blair was today accused of undermining international efforts to tackle climate change.
The environmental charity WWF said his position was becoming " indistinguishable" from that of US President George Bush.
The Prime Minister had made climate change one of the key themes of Britain's presidency of the G8 group of industrialised nations.
But WWF campaigns director Andrew Lee said that, by emphasising that targets for cutting damaging greenhouse gas emissions must not be at the expense of economic growth, Mr Blair was undermining efforts to deal with the issue.
"This is exactly the language we hear from George Bush and these statements have been very widely interpreted across the US, for example, of our Prime Minister moving towards George Bush on climate change and away from targets," he said on the BBC Radio 4 Today programme.
"There is a key issue here about international leadership. He has set himself up several times to be a strong global leader on these issues.
"Our question is: Is he a man of substance and principle on these environmental commitments or is this just nice talk?
"Not talking about targets but talking about technology is like being in a car speeding towards a brick wall. You stamp on the braking, you don't start having conversations about braking technology.
"If the price of engagement is walking away from targets, it is a price not worth having."
The Government's chief scientific adviser Professor Sir David King dismissed WWF's criticisms as "grossly unfair".
"I think we achieved an enormous amount. We now have 12 states in the United States saying they wish to engage in emissions trading to reduce greenhouse gas emissions.
"We have got all five states in Australia firm on reducing emissions. We have got a statement from the G8 saying that we will act with resolve and urgency now to meet our objectives of reducing greenhouse gas emissions," he told the Today programme.
"There is an enormous amount of interest in the topic and the reason is because we put it on our G8 agenda."
Sir David defended Mr Blair's comments that targets for reducing emissions made countries nervous about the consequences for economic growth.
"The message needs to be got across that this isn't at the expense of growing economies. I don't think that any country is going to manage a process where the suspicion is that they will need to reduce their GDP growth," he said.
The shadow environment secretary Oliver Letwin said: "The WWF is right to sound a warning note. The Government's record to date on achieving carbon reduction has unfortunately not lived up to its rhetoric - and there are now worrying signs that the Prime Minister's resolve is weakening.
"We all have to hope that he remains committed to harnessing markets and technology to reduce carbon emissions both globally and domestically - and that he accepts the need for binding reduction targets both globally and domestically.
"That is the basis upon which we can build a lasting and effective cross party consensus, which will enable us to become a low carbon economy over the next 50 years, whilst protecting jobs, economic growth and security of energy supplies."Reuse content