A leading British space expert is convinced humanity will encounter extraterrestrial life within the next five decades - though she warns they might resemble nothing more exciting than 'grey sludge'.

Dame Maggie Aderin-Pocock, from University College London's Department of Physics and Astronomy, predicts a 'positive detection' of life beyond our planet by 2075. However, stargazers hoping for something akin to the loveable creature from Steven Spielberg's 1982 classic E. T. the Extra-Terrestrial may find themselves sorely let down.

She suspects it's 'probably the most likely' that extra-terrestrials will bear a striking resemblance to colourless slime, reports the Daily Star. Nevertheless, she remains optimistic that humans might encounter a highly advanced species with superior communication technology.

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The expertmade these remarks whilst preparing to present this year's Royal Institution Christmas lectures - Britain's most esteemed public science presentations - which will explore fundamental mysteries in space research.

Her optimism is rooted in what she calls a 'numbers game' - the Drake equation. "In the whole of the universe there are approximately 200 billion galaxies," Dame Maggie said.

"And so although certain conditions were in place for life to start here on Earth, and this is the only example we have of life, I'm absolutely convinced that there's life out there because with so many stars, so many planets, why would it just occur here?"

Our galaxy houses roughly 300 billion stars, each rivalling our Sun, with planets now being spotted circling these distant suns. Dame Maggie revealed there have been 'tantalising glimpses' of potential life emerging from these far-off worlds - particularly exoplanet K218b situated 124 light years from Earth.

Researchers pinpointed molecules in the planet's atmosphere earlier this year that can only survive if some form of life exists there. Boffins hailed it as the most promising evidence yet of life beyond our Solar System, suggesting it may be ocean-covered and bustling with organisms.

NASA revealed in September what it considers the best indication of life ever discovered on Mars. Peculiar markings on mudstones in an ancient riverbed contain minerals potentially linked to Martian life.

But Dame Maggie cautioned not to expect a little green man to start waving back at Earth. She said: "Grey sludge is probably the most likely thing we're going to find." However, she added: "We might find something that does evolve and that can communicate and of course, their technology might be far superior to ours.

While basic organisms remain the most probable discovery, Dame Maggie acknowledged there's a possibility humans could encounter intelligent beings more advanced than ourselves. She emphasised any discovery of alien life would require extreme caution in its handling. "If there is any form of life we need to make sure it is totally isolated," she said." It cannot come into contact with any sort of human presence.

"Specialist laboratories are under construction to examine specimens securely on Earth, as transporting all required scientific kit to far-off worlds would prove unfeasible. Yet Dame Maggie harbours hopes that - given anticipated breakthroughs in space exploration - she might eventually relocate to the Red Planet. She said: "Some people retire and potter around their garden and my retirement plan is to potter around Mars. I think space might be a way that we unite."