Persistent attempts by China and Russia to militarize outer space will "threaten the peaceful use of space" and might see parts of low Earth orbit "completely unusable" for civilian satellites.
This is according to Air Chief Marshal Sir Michael Wigston, Chief of the Air Staff of the Royal Air Force, and General Sir Patrick Sanders, Commander, United Kingdom Strategic Command.
"A future conflict may not start in space, but I am in no doubt it will transition very quickly to space and it may even be won or lost in space," Wigston said.
"So, we have to be ready to protect and if necessary defend our critical national interests in space. If we don't think and prepare...we won't be ready when the time comes."
He said the UK's access to space remains fundamental to national security and "our way of life."
He said China intends to become the world's preeminent space power by 2045. He said this aspiration is "supported by developments in cyber, electromagnetic and kinetic systems that potentially could threaten other users in space."
He criticized China for continuing to develop direct ascent anti-satellite missiles fired from land bases to destroy American and allied satellites.
In its first test of a direct ascent kill vehicle in 2007, China destroyed one of its derelict weather satellites. The missile hit created more than 3,000 pieces of space debris larger than 10 centimeters.
"When you consider that the number of objects that size or greater is approximately 22,000 that one irresponsible action represents a significant portion of the total debris in orbit," according to Wigston.
"The increased debris density may contribute to reaching a threshold in low earth orbit that could start a chain reaction of follow-on collisions - the Kessler effect; leaving parts of space completely unusable."
He also warned "directed energy weapons" such as lasers can damage satellites to the extent that, deprived of their sensors, they tumble out of stable orbit and burn-up as they reenter the Earth's atmosphere.
Wigston said Russia keeps threatening the peaceful use of space by conducting tests with space-based anti-satellite weapons. He said Russia's "stealth satellites" seem to keep orbiting without doing anything.
He said one such Russian satellite in geostationary orbit has been moved repeatedly and is now "parked up" next to commercial satellites of other countries. Wigston is convinced this satellite is "possibly an indication of commercial and military espionage activities."
