Gordon Brown yesterday signalled that the government could toughen up its proposed climate change bill, announcing in his first Labour conference speech as Prime Minister that he was ordering an investigation into whether or not draft proposals for a legally binding 60 percent cut in carbon emissions are strong enough.

The draft bill, which is the first of its kind in the world and is set to include a legally binding target for the UK to slash carbon emissions by 60 percent on 1990 levels by 2005, has been widely praised by environmental groups but has also been criticised for failing to demand the scale of cuts demanded by the latest scientific reports.

This summer a series of parliamentary committees also argued the draft bill was not stringent enough and that stricter targets were required. Most notably the cross party Environmental Audit Committee branded the proposals "incoherent" and reserved particular criticism for the government's inadequate emission reduction targets.

Writing in its report on the bill EAC chairman Tim Yeo said, "the 2020 and 2050 targets need to be significantly strengthened, in accordance with the latest science of where we need to be to limit global warming to 2 degrees centigrade".

The government's target of cutting emissions by 60 percent had been in line with recent declarations from the International Panel on Climate Change (IPCC) that such cuts offered a good chance of curbing "dangerous" climate change.

However, many scientists have branded the IPCC's conclusions as optimistic and recent research into so-called positive feedback loops have raised fears that emission reductions in excess of 80 percent are required to stop runaway global warming whereby increased temperatures cause natural carbon sinks such as permafrost and the rainforests to begin releasing greenhouse gasses, thus further accelerating climate change.

Now Brown has recognised these concerns declaring that he is "not satisfied" with the draft bill and revealing that he is "asking the new independent climate change committee to report on whether the 60 per cent reduction in emissions by 2050, which is already bigger than most other countries, should be even stronger still".

The likelihood is that the committee will now have to recommend stricter targets in line with the latest worst case scenarios predicted by scientists or face criticism that it has placed political expediency ahead of stabilising the climate.

The Prime Minister also hinted in his speech at some of the measures likely to be deployed in order to meet the targets included in the climate change bill, announcing that he is to double the number of planned eco-towns from five to ten and committing to continued investment in clean technologies.

"By investing in energy efficiency, renewables, carbon capture, clean fuels and new environmental technologies, I want Britain to lead in carbon-free vehicles, carbon-free homes and carbon-free industry," he said. "And I want the new green technologies of the future to be the source of British jobs in British businesses."

Brown's speech comes a crucial week for global climate change negotiations as world leaders meet today at the UN in New York to discuss climate change strategy ahead of the crucial meeting in Bali this December where negotiations for a post-Kyoto Treaty will formally begin.

Those talks are to be followed later this week by a controversial meeting of the world's major emitters hosted by President George Bush. The US administration claims the meeting, which was proposed earlier this year, is intended to also support the Bali negotiations, however critics have argued that the setting up of parallel talks are intended to undermine the UN process.