The new environment secretary has been challenged to speak up for his department amid claims it has become marginalised in the nuclear power row.
Mr Miliband was made environment secretary in the reshuffle
David Miliband came under pressure in questions from his Conservative shadow, Peter Ainsworth.
Downing Street said there was no "cost free" way to tackle the energy gap amid criticism nuclear was too expensive.
Mr Miliband has said he is open-minded on nuclear energy and pledged to speak up for his department.
He took over from Margaret Beckett at the Department for Environment, Food and Rural Affairs in this month's Cabinet reshuffle.
Meanwhile it has been revealed there have been 57 occurrences at existing nuclear sites around Britain since 1997, 11 of which were serious enough to be classed as "incidents" or "serious incidents", according to figures released by the government.
Problems ranged from radiation leaks and machinery failures to contamination of ground water or employee clothing and a fire.
A DTI spokesman said: "Few of the documented 'incidents' are of any serious danger. Even the most serious incident - the widely reported leakage at the Thorp plant detected last year - was contained and posed no threat to staff, public or environment."
The prime minister's official spokesman meanwhile said the government would look at "everything" in its search to secure the future of energy in the UK.
"There isn't a cost-free option. There's no one-club, free, solution to this. We have to look at everything," the spokesman said.
"There is an energy gap, there is an issue about not meeting the CO2 emissions targets and therefore we have to address it."
This week Tony Blair announced nuclear power was "on the agenda with a vengeance".
But several in the Cabinet are members of the Socialist Environment and Resource Association (Sera), which is anti-nuclear.
They include Mrs Beckett, who is now foreign secretary, Labour chairman Hazel Blears, Welsh Secretary Peter Hain and Mr Miliband.
Sera also counts among its members key Gordon Brown allies including Ed Balls, recently elevated to a job at the Treasury, and Andrew Smith.
But it is Mr Miliband's name on the list of supporters that will raise most eyebrows.
It was widely speculated in the wake of the reshuffle Mrs Beckett was moved from Defra to the Foreign Office partly because of her opposition to nuclear power.
In the wake of Mr Blair's comments Mr Miliband said: "I am open-minded about how we meet the climate change challenge.
"Obviously the benefit of nuclear power is that it emits zero carbons but obviously there are costs associated with nuclear power and there are also waste issues, which are very important."
Former Environment Minister Elliot Morley, who left the government in the reshuffle, used an interview with the Guardian to highlight the costs issue: "To have new nuclear power is going to involve very large sums of money.
"If nuclear power was so great then you would have the private sector willing to invest in it.
Mr Blair's comments were widely seen as pre-empting the outcome of the ongoing energy review.
Sera's submission to the review includes a call for "no new nuclear power stations".
Another former Environment Minister, Michael Meacher, and Mr Morley have joined forces submitting a parliamentary motion saying the case has not been made to begin building new nuclear power stations.
Lib Dem environment spokesman Chris Huhne said he believed nuclear power would be a "wrong turning".
"You can see that not a single nuclear power station has been built anywhere in the world without lashings of government subsidy since Three Mile Island and Chernobyl," he said.