Young people who want to "change the world" should become scientists to help find ways to combat global warming, Tony Blair told a meeting in Oxford today.

The Prime Minister - in the latest of a series of speeches on the key issues facing the country - said the sector was vital to keeping the UK competitive.

He seized on the publication of the Stern report on challenges posed by global warming in his bid to enthuse a new generation to get involved.

Speaking at the King's centre, in Osney mead, he said: "It might have been a gloomy document. Actually, it wasn't - it was full of can-do optimism.

"One of its implications was that if, as an idealistic young person, you wanted to change the world, then become a scientist."

Yesterday Mr Blair was in the county to visit the UK's biggest science project for 30 years.

The Government has put more than £200m into building the giant Diamond Light Source at the Harwell Science and Business Campus.

When it opens next year it will employ 330 staff and attract several thousand scientists from UK universities and research labs.

The medical research charity Wellcome Trust has put another £35m into the machine, which will produce X-rays 100 billion times brighter than a standard laboratory X-ray machine.

The machine is a super microscope using an intensely focused light source housed in an area the size of five football pitches.

Mr Blair said: "This new world-class facility shows the importance this country attaches to science and scientists.

"This is exactly what Diamond Light Source will help us achieve in many fields, from developing new drugs to tackling climate change.

"Our future prosperity rests more than ever before on the hard work and genius of our scientists and how we harness their research to deliver improvements in all our lives.