The Prime Minister said in an interview with The Times that there should be a more mature attitude to science in Britain. "It is time to speak up for science," he said in advance of a substantial speech on the subject on Thursday.

Mr Blair gave warning that research work would be lost to Britain and Europe and go elsewhere in the world if animal welfare activists and other protesters were allowed to get away with stopping projects that could save lives. He called for an end to the air of suspicion and mistrust that sometimes surrounded the work of scientists and the misplaced fears and ignorance it often generated. Mr Blair said there were huge opportunities in science, for medical progress and for dealing with some of the great environmental and economic challenges.

His speech, in which he will promise to continue increasing investment in research and development, has been planned since he visited high-tech projects in India at the turn of the year.

He said: "I was struck in India by the very close links between enterprise and science and the fact that the Indians were openly saying that they felt that some of the anti- science attitudes in the developed economy were giving them real opportunities they were determined to exploit."

Mr Blair said that there were obviously ethical questions over some research that had to be addressed by politicians and society as a whole. "But it is completely unacceptable for people to try to disrupt and destroy the legitimate research on which these issues will ultimately be judged."

The Prime Minister is privately furious at the actions of protesters which have resulted in work being held up on research into genetically modified foods, and at disruption that could threaten a neurological research project in Cambridge aimed at helping sufferers of Alzheimer's disease. He is angry over the regular description of GM foods as "Frankenstein foods", and at the way science was blamed for the BSE emergency. "BSE was not caused by bad science but by bad practices," he said.

"Some of these protests have been completely over the top," Mr Blair said. "There are huge challenges and opportunities we have to face up to. It is time to defend science, to make clear that the Government is not going to allow misguided protests against science to get in the way of confronting the challenges of making the most of our opportunities."

In his speech on Thursday, Mr Blair will speak of his objective to persuade more young people to take up mathematics, physics and engineering at school and university. He will say that scientists should be applauded and admired and should not have their work denigrated. He will speak of increasing co-operation between countries on research, saying that he does not want a "little Britain approach" to science.

Mark Matfield, director of the Research Defence Society, which speaks up for scientists involved in animal experiments, said last night: "We welcome this hugely. Tony Blair has always been very pro-science and pro-scientist, and we were impressed with the way he refused to mince words over Huntingdon Life Sciences.

"All our research shows that it does make a very significant difference to public attitudes when you see political leaders speak out on these issues."

Mr Blair was right to say research would go abroad if the conditions were not right, Dr Matfield said. What was more, many other countries had less rigorous ethical standards. "Here in Britain, we manage to combine top quality science with very high ethical standards, but other countries, the 'tiger economies', do not balance those in the same way we do," he said. "We walk a very careful line, and we would not want research to be driven to places where the standards are not those that we approve of."

Guy Poppy, of Southampton University, a member of the pro-GM panel Cropgen, said: "I think most of the public agree with Mr Blair. They want more information on the GM issue to make up their minds, and that is not helped when people destroy the trials that have been set up to determine exactly that. That's something we have always thought Tony Blair and other politicians should be clear about stating, and we're delighted that he's doing so.

"I think speaking out like this also means a lot to the scientists and people involved in the field. They realise there is a figurehead who is prepared to listen and to support them."

An exclusive interview with Tony Blair will appear in The Times tomorrow.

Five priorities

GM crops: Field trials testing the impact of genetically modified crops on biodiversity are under way. There will be pressure from anti-GM campaigners to keep the moratorium on commercial planting.

Animal rights extremism: The Government has bailed out Huntingdon Life Sciences but the problem of violent protests against the use of animals in medical research remains acute.

Cloning and stem cells: Human reproductive cloning is banned but research into embryonic stem cells is allowed in Britain. The rules allow more work to be done here than in other countries; leading scientists are moving here to pursue their research.

Genetic privacy: Insurance companies are to be allowed to demand the results of certain genetic tests. Most other countries have elected to keep these data secret.

Funding: This has improved substantially since 1997 but many laboratories are dilapidated; universities can rarely compete with American counterparts when it comes to academic salaries.