The environment minister Michael Meacher was at loggerheads with Clare Short last night over the purpose of the forthcoming Earth Summit in Johannesburg.
Mr Meacher had already incurred Downing Street's wrath when he attacked the Government's poor record on green issues.
But tensions within the Government were further underlined by Ms Short, the Secretary of State for International Development, in an interview on the Johannesburg agenda.
"This isn't an environmental summit," she said, in an apparent rebuke to Mr Meacher's stated priorities. "It's a summit about sustainable development. The biggest challenge to the world is to guarantee to the poor of the world development in a planet that we keep sustainable."
Asked on BBC Radio 4's The World This Weekend about Mr Meacher's comments, Ms Short said: "The summit isn't about Britain's transport policy. It is about the sustainable management of the whole world's resources. To focus it all on such issues in the UK is not to talk about what the main issues of the summit will be."
Earlier, Mr Meacher, who fought off an attempt by No 10 to exclude him from the British delegation to the summit, had denounced Labour policies on transport, house-building and airports.
He complained that the Government had not faced up to the scale of the threat to the environment and depicted himself as a "lone voice in the wilderness" on the subject.
But a Downing Street spokeswoman said: "The Government is committed to sustainable development to ensure we have a planet worth living on for our children and their children."
She said that one of the reasons the Department for Environment, Food and Rural Affairs was created last year was to put the issue "at the heart of our policy-making".
One Whitehall source claimed last night that the Environment minister was "increasingly behaving like an unguided missile".
Ms Short confirmed she had volunteered not to attend the summit during discussions on reducing the size of the British delegation, but added: "It was the view of most of my fellow ministers that I needed to be there because the developing countries will be in the lead in this summit."
In his interview with The Sunday Times, Mr Meacher said: "I make no bones about it. I don't think the Government, as a whole, is ready to take the magnitude of the decisions I think are necessary."
Asked if he believed Tony Blair understood the threat to the environment, he replied: "I hope so. One is like a lone voice in the wilderness."
Malcolm Bruce, the Liberal Democrats' environment spokesman, warned yesterday that ministers could no longer afford to ignore Mr Meacher. "The row over Michael Meacher's role in the Government's delegation to the summit has strengthened his position and presents an environmental challenge to Tony Blair," he said.
"Mr Meacher has now become virtually unsackable."