Aliens are alive and well in the rest of the cosmos - and they could already be tuning into vintage human radio broadcasts, according to leading scientists.

For the first time in history, the dream of searching for signs of life in other solar systems is on the list of achievable and planned human endeavours, mostly because around 280 planets have been discovered orbiting alien stars.

Experts involved in the study of these alien worlds, and in the quest to find more, told the Government yesterday they were convinced that life exists elsewhere in the universe.

Most of them are also convinced that intelligent life will be lurking among the bacteria, microbes and lowlier unearthly bugs.

They gathered yesterday at the Department of Trade and Industry in London to meet the Science Minister, Malcolm Wicks.

They told him that there have been remarkable advances over the past few years in looking for stars that have planets and said we are beginning to find Earth-like planets that might have liquid water, thought to be a key prerequisite of life.

The straw poll of the experts, suggesting they were all convinced of the existence of alien life, was "very interesting," said the Minister. "As a lay person, that is how I would vote as well, given the vastness of space."

Prof Glenn White of Open University said that a European Space Agency mission called Darwin, a flotilla of telescopes due for launch in 2018, will scan 500 stars over five years within a distance of 60 light years and study the light from 50 alien planets to seek vital signs.

"Once the mission gets up, we are pretty sure that, if there is life out there, we are going to have an extremely high probability of telling you whether life has started on a planet," said Prof White. "Around 2020 we will have very definitive answers."

His Open University colleague, Prof John Zarnecki, said that in 2015 a mission will land on Mars to dig two metres into the surface and use a package of instruments to look for life signs, "biomarkers".

And he had high hopes for a future mission to the icy Jupiter moon Europa too. "My position is very simple," said Prof Zarnecki, who has helped to land a probe on Saturn's moon, Titan. "We will find extinct or some life in the solar system or extrasolar systems. We shall find life on Mars in 2015 and on Europa in 2023."

Dr Ian Stevens of the University of Birmingham said that life got started early in the life of the Earth and "my guess is life is common out there".

And Dr Michael Perryman, formerly of the European Space Agency, pointed out that it is already possible to analyse the light from an alien planet for life signs, "which is staggering".

Although the only scientist present who doubted there was intelligent alien life, arguing the circumstances of the Earth are too special, Dr Perryman said he would not be surprised if, in a few months, biologists reported they had found the spectrum of chlorophyll, suggestive of plant life.

"Don't underestimate what a huge revolution this whole business of finding planets has been in science," he said. "Everyone now is working on this."

He added that aliens could now be eavesdropping on us. "As from 1927, we have been propagating outwards from Earth, a very specific indicator of our existence."

These radio waves are now 80 light years away. "That is going to encompass many hundreds of potentially habitable planets," he said. "It is not just a one way process. If there is intelligent life out there, they sure as hell know we are here."