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President Barack Obama has today signed an executive order, put in place by his predecessor, President Bush. The move has been condemned by conservative and religious groups, but many scientists see this as the start of a new, more optimistic era for a science that's promising cures for conditions from Alzheimer's disease to blindness.

Some American scientists could hardly contain themselves: "I feel vindicated after eight years of struggle, and I know it's going to energise my research team," one said this morning. He was looking back over a Bush presidency ever mindful of those who oppose the use of human embryos to create "lines" of stem cells. George Bush restricted stem cell scientists, allowing them to use federal money for research on only on a very limited number of cell lines.

With today's move, president Obama has reversed all that. Though scientists still can't actually make embryos to use their stem cells, they can now buy any stem cell line they want. This is a huge injection of confidence into stem cell science, and that confidence is almost as important as the practical reality of gaining access to a greater range of cell lines.

So will this speed up new treatments?

Well, not immediately. In the Bush years, some scientists found ways round the restrictions. They sought private backing for research not allowed using tax payers' money, or looked at ways to explore their scientific goals without using stem cells from embryos. So today's step in itself may not mean an immediate glut of new science, thought the extra money set to become available under president Obama's push to expand medical sciences with his economic stimulus package is expected to have a big impact.

And the science itself is already forging ahead. Almost every day there are advances in the scientific journals, which slowly but surely offer the promise of a future where we can replace worn out tissues damaged by disease or ageing - or even perhaps one day, replace whole organs.

There is still a debate within stem cell science over the hurdles researchers must straddle when they want to test potential treatments in large numbers of patients. One company apparently had to submit 20,000-odd pages of documentation to secure approval for its clinical trial. Though other stem cell scientists say theirs is such a new area of research and the dangers still so hard to quantify, that it's right for their work to be tightly regulated. What they fear most is a tragic outcome in a patient that stalls the whole field.

There are now fears that this very different approach in the US will offer an inspiring environment for young British scientists, and that we could even see a new "brain drain" of UK researchers heading for the states, or American researchers who left during the Bush years going back home. It's really too early to say if that's happening, or not. What is certain is that there will be a huge amount of money available to scientists in the US, billions of dollars are earmarked for the as part of the stimulus package. The UK's established stem cell scientists might have roots firm enough that they resist the urge to wander off. But younger PhDs, just starting out, might see the US as a more attractive option - with the prospect, one scientist told me today, of $2-3m grants for researchers in California - where stem cell science is receiving massive state funding.

And all of this puts put extra pressure on the UK government to make sure British science remains competitive. Ministers have talked a lot in recent weeks about supporting science - with ten days ago stressing the importance of our science base in re-creating our economy. And today, at the start of , science minister Lord Drayson is calling on industry to back the creation of more , to go into schools and help inspire our young people. The prime minister might contemplate how best to make sure that they don't all drift overseas once they graduate. Stem cell science is getting more money than other areas of scientific research, indeed more money is going into science in general... but whether it will be enough to keep our young people here is another question...