A new exhibition on the Soviet Union's space programme opening in London this year will be the biggest of its kind ever held outside Russia, organisers said on Thursday.

Among the artefacts on display will be the Vostok-6 capsule which carried Valentina Tereshkova, the first woman in space, safely back to Earth in 1963.

It will also feature an original 1957 model of Sputnik, the world's first artificial satellite, which triggered the space race with the United States when it was launched into orbit that year.

The Soviet Union followed the global success of Sputnik by launching the first animal, man and woman into orbit in just six years before being beaten to the Moon by US astronauts in 1969.

Visitors to "Cosmonauts: Birth of the Space Age" at the Science Museum will also be able to see exhibits from the Soviet manned Moon programme, details of which were kept secret for decades.

Among them is one of the five-metre (16-foot) high LK-3 lunar landers, which were tested but never sent to the Moon.

Soviet cosmonaut Alexei Leonov, the first person to carry out a spacewalk 50 years ago on March 18, 1965, spoke at a press conference announcing the exhibition alongside Science Museum director Ian Blatchford.

"'Cosmonauts' is a once-in-a-lifetime exhibition that has taken years of dedication and skill from the Science Museum team to make a reality," Blatchford said.

"Virtually none of these objects have ever left Russia," he added.

The exhibition, which opens on September 18, is being organised with the Russian space agency Roscosmos.