Tony Blair has been accused of giving "patchy" and "muddle-headed" leadership on climate change in the UK by his own sustainable development adviser.
And the PM's green views, in a Sky News interview, were "completely wrong", Jonathon Porritt told the BBC.
Mr Blair had said he would not give up flying, doubted any politician would tell people not to fly, and questioned the impact of UK-only climate action.
No 10 later said Mr Blair would offset emissions from his holiday flights.
'Energy efficiency'
That decision was welcomed by Mr Porritt, chairman of the sustainable development commission, which reports directly to Mr Blair.
However, he said it was wrong to believe technology "could get us out of the mess".
"It's like telling people you shouldn't drive anywhere"
Mr Porritt said: "The irony here is that the prime minister's leadership, internationally, has been exemplary."
"He's done more than any other world leader to bring people to a sense of awareness about the importance of climate change. But here in the UK, his leadership has been patchy, and frankly muddle-headed."
During the Sky News interview earlier on Tuesday Mr Blair was asked whether he would give up long-haul flights.
He replied: "I personally think these things are a bit impractical actually to expect people to do that.
"I think that what we need to do is to look at how you make air travel more energy efficient, how you develop the new fuels that will allow us to burn less energy and emit less."
'Personal efforts'
He added: "You know, I'm still waiting for the first politician who's actually running for office who's going to come out and say it [that people should not fly] - and they're not.
"It's like telling people you shouldn't drive anywhere."
He added later at a Downing Street press conference: "There are masses of things we can do personally."
HAVE YOUR SAY
Mr Blair also said: "But I'm not going to be in the situation of saying I'm not going to take holidays abroad or use air-travel. It's just not practical".
Environment Secretary David Miliband said the prime minister was setting an example by off-setting his air travel and using renewable energy in his house.
But Friends of the Earth head of campaigns Mike Childs said: "It's disappointing that Tony Blair is refusing to set an example on tackling climate change.
"Aviation is the fastest growing source of carbon dioxide in the UK.
"But rather than taking steps to curb the rise in air travel, the government is encouraging it by giving the aviation industry multi-billion pound tax breaks and allowing UK airports to expand."
Conservative MP John Gummer, who co-chairs his party's quality of life policy group, said: "He [Mr Blair] can expect nothing at all from the electorate unless he himself does what he knows is right.
Liberal Democrat environment spokesman Chris Huhne said ministers needed to re-examine their environment policies.
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