Scientists searching for alien life should get governments and the UN involved lest we unwittingly contact hostile extraterrestrials, a British astronomer has warned.

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Do aliens exist? And would they be friendly?
The caution comes as more experts argue that the search for intelligent life should be stepped up.

Mr Marek Kukula, public astronomer at the Royal Observatory in Greenwich, said: "Part of me is with the enthusiasts and I would like us to try to make proactive contact with a wiser, more peaceful civilisation."

But he warned: "We might like to assume that if there is intelligent life out there it is wise and benevolent, but of course we have no evidence for this.

"Given the consequences of contact may not be what we initially hoped for, then we need governments and the UN to get involved in any discussions," he told The Sunday Times.

This week a two-day conference is being held at the Royal Society in London, titled, 'The detection of extraterrestrial life and the consequences for science and society.'

There is also an astrobiology conference in Texas in April at which new methods of detecting aliens will be discussed.

Douglas Vakoch, director of interstellar message composition at the Search for Extraterrestrial Intelligence (SETI) Institute in California, told the paper: "My personal view is that being more active is a worthy strategy. There is more serious talk of it, though not at the institute level."

Professor Simon Conway Morris, a Cambridge University evolutionary biologist, will be talking at the Royal Society on 'Predicting what extraterrestrial life will be like - and preparing for the worst."

He thought that, given that the principles of Darwinian evolution should be universal, it was "inevitable" that intelligent life would have developed elsewhere in the universe given the right environmental conditions.

"If that is correct - and it applied to manipulative skill - then that suggests there should be alien technologies," he said.

Some scientists are puzzled as to why no messages have been sent back even though humans have been transmitting radio and television signals for the last century.

Prof Conway Morris reasoned that if he were in their shoes "I'm not sure I'd answer the telephone."