A former military helicopter pilot is to become the first UK astronaut to visit the International Space Station (ISS).
Major Tim Peake will live and work on the space station for six months. He will carry out a science programme and take part in a European education initiative before and during his mission.
He is one of six astronauts selected from more than 8,000 hopefuls. The flight is expected to take place in November 2015.
Major Peake , 41, has undergone 14 months of rigorous training, which has included survival courses and exercises under water and underground.
The former British Army Air Corps helicopter pilot, who graduated as an astronaut three years ago, will be the first UK astronaut in space for more than 20 years.
Speaking after his selection, Major Peake said: "I applied to become an astronaut with the European Space Agency because I believe for me it's a unique opportunity in my life to become part of a team that can have such a positive impact on society.
"I believe humankind faces some enormous challenges this century, and the space arena is going to be fundamental in overcoming some of those challenges."
It is hoped Major Peake, who tweets with the handle @astro--timpeake , could even match the popularity of David Bowie fan, Commander Chris Hadfield.
Cdr Hadfield, from Canada, was his country's first professional astronaut, but gained a legion of fans on the Soyuz space capsule mission to and from the ISS, by performing a cover of the Bowie classic, Space Oddity.
He now has close to one million followers on Twitter.
Major Peake will face his own personal challenges including getting used to life without gravity, and his family.
His living quarters during the mission will be barely the size of a phone box.
The Prime Minister described Major Peake's selection as "a momentous day" for the country.
"It is a great sign of our thriving British space sector, which has seen real growth thanks to our world-class research, and now supports nearly 30,000 jobs," David Cameron said.
"What an achievement that Tim was picked for this historic role from over 8,000 applicants from around the world.
"I am sure he will do us proud and I hope that he will inspire the next generation to pursue exciting careers in science and engineering."
Space writer Nick Spall added: "Space can make lots of money. The satellite industry's very successful, but space isn't just about building satellites or building robots to explore the solar system.
"It's also human space flight as well, and all the developed countries, and in particular the emerging developed countries - China, India - are committing themselves to human space flight, so it's a case of Britain joining in."
The first Briton in space was Sheffield-born chemistry graduate Helen Sharman in May 1991. She took part in the Soviet mission Project Juno, spending eight days conducting scientific experiments at the Mir Space Station.
Huge financial costs meant that Britain has in the past rejected the notion of manned space flights. A handful of Britons have flown on the US space shuttle, but there have been no "home-grown" UK manned space missions.
Although Helen Sharman has been into space before, Major Peake will officially be the first British astronaut.
The others either took American citizenship or their missions were privately funded.
But when his Soyuz rocket blasts off from Kazakhstan he will be focused more on where he is going than where he has come from.