"This is the first comprehensive set of proposals to reduce carbon emissions from every sector of the economy ever produced by any British political party," said the party's environment spokesman Chris Huhne.

"We can no longer believe that a 60 percent cut in carbon emissions is enough, as the government claims," he added. "No one believes it, not even ministers. The science says it needs to be more than 80 percent."

The policy would raise 12 billion pounds from tolls on lorries using motorways to pay for a doubling of investment in rail transport, with a new high-speed north-south rail link a likely priority.

Other measures would include "green mortgages" to pay for thick insulation in roof lofts and one billion pounds spent on flood defences.

"With these plans we can restructure the economy towards a basis built on renewable energy, not on fossil fuels," said Huhne.

"It's an enormous economic change, but an economic change in line with changes that we have seen in the past, for example moving from steam power to the petrol engine, from gas light to electric light. It can be done."

But with the party trailing badly in the polls on support of around 15 percent, the likelihood of the new policy becoming law remains slim.

A Populus survey in the Times newspaper on Monday found that 69 percent of those asked agreed that the Liberal Democrats "are basically a protest vote because realistically they have no chance of government."

A poll at the weekend put "Ming" Campbell's personal rating as low as 4 percent, while newspaper cartoonists on Monday depicted the 66-year-old leader as a lame duck or as a pensioner leaning on a Zimmer frame.

The Daily Telegraph called for Campbell to "go at once".

"The soothing, forgettable, bathwater-warm Sir Ming has neither the character nor the energy for the task", said the right-of-centre daily.

Vernon Bogdanor, professor of government at Oxford University, told BBC radio the problem facing the Liberal Democrats was not, as was once said, that they had no policies, but that they had too many.

"What the party needs is a very clear sense of direction -- the sort of thing that Tony Blair gave to Labour to make it New Labour and that Margaret Thatcher gave to the Conservatives," he said.