Artist's impression of the Galileo satellite (Picture: ESA).
Britain has given up efforts to gain access to the EU's Galileo satellite navigation system for defence and critical national infrastructure purposes, after being frozen out by Brussels because of Brexit.
Prime Minister Theresa May confirmed the UK will instead aim to build its own Global Navigation Satellite System, at a cost estimated by independent experts at £3-£5 billion.
It is unclear whether the UK will get back the £1.2 billion it sunk into Galileo, a rival to the US GPS system that will not only support mobile phones and satellite navigation but also provide vital location information for the military.
Speaking during her visit to the G20 summit in Argentina, Mrs May said: "I have been clear from the outset that the UK will remain firmly committed to Europe's collective security after Brexit.
"But given the Commission's decision to bar the UK from being fully involved in developing all aspects of Galileo, it is only right that we find alternatives.
"I cannot let our armed services depend on a system we cannot be sure of. That would not be in our national interest. And as a global player with world-class engineers and steadfast allies around the world, we are not short of options."
Mrs May sought to increase pressure on Brussels in August by committing £92 million to explore a possible home-grown alternative, arguing it was not acceptable for the UK simply to be an "end user" of the EU system, shut out from security discussions and contracts.
The UK is now expected to work with the US and other partners of the "Five Eyes" intelligence alliance, comprising Australia, Canada and New Zealand.
Mrs May said any new system must be compatible with GPS so the two systems can cover for each other if one is subject to attack.