Intelligent extra-terrestrials almost certainly exist on distant planets beyond our solar system, leading British astronomers told the government yesterday.

The scientists expect that the first evidence of primitive alien life, such as microbes and vegetation, will emerge within 10 years, with more substantial finds following future space missions.

The experts, from high-ranking UK universities and research institutes, were gathered in London by the science minister, Malcolm Wicks, to describe the latest advances in the search for distant, habitable planets capable of harbouring life.

A recent revolution in technology means astronomers can now spot Earth-like planets orbiting faraway stars, raising the chances of alien life being found. By analysing reflected light, it is becoming possible to find any that may host vegetation and breathable atmospheres.

"Twenty years ago we only had one solar system to study and that's the one we live in. But since then, there's been an explosion in the number of planets outside our solar system that we've been able to detect," said Professor Keith Mason, chief executive of the Science and Technology Facilities Council and former head of space physics at University College London. Some 200 planets have been detected orbiting stars other than the sun.

Scientists this year announced the discovery of a warm, rocky "second Earth" circling a distant star called Gliese 581, about 20 light years away in the constellation of Libra. Crucial measurements of the planet's surface temperature range revealed it was able to hold liquid water, believed to be a prerequisite for life.

In 2015, the European Space Agency will launch a mission called Darwin, a cluster of four orbiting telescopes that will scour the heavens for life-bearing planets. For five years, the telescopes will peer at 500 stars and conduct spectral analyses of the 50 most promising planets it detects.

"You can be pretty sure that if there's life out there, we've a good chance of being able to say so," said Glenn White, head of astrophysics at the Open University and a scientist on the Darwin project.

Our own existence may already have come to the attention of any aliens who are peering in our direction across the depths of space. Since the advent of radio waves, stray signals have leaked from Earth and travelled as far as 80 light years into space, far beyond the closest stars.

"If there's intelligent life out there, they sure as hell know we're here," said Michael Perryman, an astrophysicist at the European Space Agency.

The seven scientists, who included Ian Stevens, head of extrasolar planets at Birmingham University, and Suzanne Aigrain, of Exeter University, all believed that life existed elsewhere. Only Dr Perryman believed humans to be the sole intelligent beings in the universe.