SCOTTISHPOWER received a pat on the back from the World Wildlife Fund (WWF) last night after being named the UK's greenest power company - but the highly respected environmental organisation warned that the industry should still be doing more.

WWF's Generating Climate Change report - released ahead of the government's energy review later this week - ranked the Glasgow- based utility top of the UK's six largest power companies. Scottish & Southern Energy (SSE) - the group's Perth-based rival - came in third.

The companies were rated according to their performance on greenhouse gas emissions, energy efficiency and plans for renewable energy. ScottishPower was found to have reduced its emissions by more than 11 per cent per KWh generated in 2005, the biggest cut out of all the main UK power companies.

Dr Richard Dixon - the director of WWF Scotland - acknowledged ScottishPower's progress, but added that there was still a lot more to do to address climate change.

"While all the power companies can do more, it is great news to see Scottish Power leading the field in taking action to reduce emissions," he said. "However, this report shows that overall the power sector is doing little beyond trying to meet government targets."

The report has been timed to add poignancy to the government's energy review - its second in three years.

Strong hints from the Prime Minister, Tony Blair, have suggested that a new fleet of nuclear power stations will be central to its recommendations - something Dixon has reservations about.

"ScottishPower deserves praise for its reductions in emissions over the last year, but look at the bigger picture and there is still a long way to go," he warned. "It is no coincidence that the company most involved in nuclear power, EDF Energy, performs worst overall."

He added: "If we go with new nuclear power stations, it will take about 20 years to get them built, at a cost of anything between GBP 10-20 billion. And then it will only reduce carbon emissions by 8 per cent. Our view is that the government should stick with the conclusions of the previous review in 2003 - build renewables."

The report goes on to praise companies with a strong commitment to investment in renewable energy, with ScottishPower pledging more than GBP 1bn up to 2010 - not including its US wind farm operator PPM Energy.

Dr Dixon said: "The government needs to set much more ambitious targets to increase and diversify the use of renewable energy, cut energy waste, and in turn, reduce carbon dioxide emissions."

The UK power sector's emissions have soared by 15 per cent since 1997 with total emissions rising by 2.3 per cent in the same period. In Scotland, the energy sector was responsible for 37 per cent of climate change emissions in 2003, 3 per cent higher than in 1990.