Chancellor Gordon Brown will try to seize back the green agenda from the Tories when he calls for worldwide action to tackle climate change.
Mr Brown will suggest steps businesses can take to save energy
He will highlight the government's role in setting new European Union standards on carbon dioxide emissions.
But the Green Alliance, the group hosting Mr Brown's speech, criticised the government's green credentials.
The group said the Conservatives' plans for new aviation taxes showed that they were more radical than the government.
'No credibility, no influence'
The chancellor will dismiss Conservative leader David Cameron's ability to take a lead on green issues in the European Union because of his party's euro scepticism.
"Let us also be clear: only a government fully committed to the UK's role in Europe can show such leadership," he will say.
"Euro-scepticism and continent-wide environmental action are at odds with each other.
"A government ambivalent about the UK's future in Europe and allied to the most reactionary forces in the European Parliament would have no credibility, no influence and no achievements."
Following the Tories' launch of a bold package of proposals to tax frequent fliers, Mr Brown will criticise "ill-conceived" and "unworkable" measures.
"Changes must be considered, costed, credible and consumer friendly not ill-conceived, short-termist, unworkable and unfair."
But Mr Brown's attempts to regain the initiative were undermined when a spokesman for the organisation hosting his speech said the Conservatives' proposals were more radical than the government's.
Stephen Hale, director of the Green Alliance, said the Conservatives' proposals on aviation fuel "would take them ahead of where the government are at present, if they see it through".
He told ITV's The Sunday Programme: "David Cameron is good news. But the concern is that every time he makes another photo-call, our expectations rise of what the Conservatives would actually deliver."
Mr Brown will also set out steps individuals and businesses can take to save energy in their daily lives.
"People want to make the right choices and they want help to take the right decisions.
"Government must provide practical help with, where ever possible, incentives in preference to penalties," he will say.
On Tuesday the government will launch its Climate Change Bill, which puts the government's long-term goal to reduce carbon dioxide emissions by 60% by 2050 into statute.
However, the Bill does not include plans for strict annual targets for emissions reductions, as demanded by the Tories.