Gordon Brown will today announce ambitious targets to increase the numbers of pupils studying sciences and maths in state schools, as part of a drive to ensure Britain produces "the great scientists of tomorrow".

The Prime Minister will argue that investment in science is key to Britain's future competitiveness and will signal his ambition to shift the UK economy away from its over-dependence on financial services and towards science and technology.

In a speech in Oxford, the PM will promise not to let science become "a victim of the recession", vowing to protect funding for science from competing demands for Government support during the downturn.

And he will announce initiatives to encourage graduates with science, maths and IT degrees who lose their jobs during the recession to retrain as teachers, as part of a drive to ensure almost all state schools offer physics, chemistry and biology as separate subjects within five years.

Mr Brown will say: "The time has come to build a society that seeks high-value engineering not financial engineering. A country whose young people are more inspired by those who give to the world, than by those who take from it.

"And a nation that values Britain's great history of scientific achievement and that backs Britain's capacity for scientific discovery.

"We have a scientific record to be proud of. The question now is how we build on this strength to make Britain the best country in the world in which to be a scientist in the months and years to come."

Mr Brown will set out a "national ambition" for Britain to educate the next generation of world-class scientists.

He will offer a guarantee that within five years, 90% of all state schools will offer the "triple science" option of single-subject teaching of physics, chemistry and biology. At present, only 32% of state schools offer triple science - up from 22% in 2005.

The aim is to at least double the number of state school pupils taking the three science subjects from its current level of 8.5% over the next five years, involving 100,000 children a year.

And Mr Brown will set a new target to increase the numbers of young people sitting A-level maths from 56,000 now to 80,000 by 2014.

He will recognise that mainstream comprehensive schools have suffered from a lack of specialist science teachers able to take single-subject classes and stretch the brightest pupils.

To address this shortage, graduates made redundant in companies working in science, technology, engineering, maths and IT will be offered personalised support from education consultants to consider the option of retraining as teachers.

Mr Brown will promise to maintain the "science ring fence" which guarantees that state money earmarked for science is protected from competing demands.

"Some say that now is not the time to invest, but the bottom line is that the downturn is no time to slow down our investment in science," the PM will say.

"We will not allow science to become a victim of the recession - but rather focus on developing it as a key element of our path to recovery.

"That is why we will maintain the ring fence we have placed around science funding."

Mr Brown will also promise to "promote a positive public debate about the proper role of science in the service of humanity" in order to improve public understanding and awareness of science.