Controversial climate change sceptic Lord Christopher Monckton has mocked Prime Minister Julia Gillard on the eve of the Government's carbon tax announcement, saying Australia will become a "third world banana monarchy" if it introduces the tax.

Speaking at a rally of those against the tax in Sydney's Hyde Park on Saturday, Lord Monckton said the Prime Minister was destroying her own country.

"If this carbon tax goes through then it's bye-bye Australia, it's been nice to know you," he told the crowd of hundreds.

The rowdy crowd continually cheered and there were chants of "ditch the witch" and "no more Greens".

Lord Monckton, who is visiting from the UK, repeatedly used a mock Gillard accent to say he agreed with the Prime Minister, but only when she said "the Government I lead will not introduce a carbon tax".

He said there was no need for the tax and that the prime minister should listen to her people.

"Julia darling, listen to the voice of the Australian people gathered here in Sydney on this beautiful, sunny but rather cold day - we could do with some more global warming," he said.

"First of all there's no need for it, you may have noticed the planet has not been warming at anything like the rate that they predicted, it isn't happening and it isn't going to happen - they got the sums wrong.

"What we're going to do is get the sums right and the way we're going to do it is through the ballot box."

Lord Monckton says he still holds out hope Ms Gillard will not introduce a carbon tax. He says he will be watching Sunday's announcement closely.

"Even if the consequences were to be as dangerous as some have suggested, it would still be more cost effective to do nothing and to adapt in a focused way to those consequences, than to try to do anything now, to wreck our economies," he said.

Lord Monckton also took a swipe at some ABC presenters, who he claimed were "vilely rude" to him during interviews this week, and admitted to having been unknowingly pranked by comedy team The Chaser.

He said he believed the ABC was a supporter of totalitarianism and should no longer be publicly funded.

Late last month, Lord Monckton put a quote from the Federal Government's chief climate change adviser, Professor Ross Garnaut, next to a Nazi swastika, calling him "fascist" for suggesting people accept climate science.

He later admitted it was "catastrophically stupid" to compare the prominent Australian economist to Adolf Hitler.

The Government will unveil all the details of its emissions trading scheme tomorrow, which will start with a fixed price for carbon from July 1, 2012, followed by a floating price from 2015.

It has been reported the starting price will be $23, with fuel for households and small business exempt and the full price only applying to about 500 of the nation's biggest polluters.

- ABC/AAP